I was really surprised to discover this bug a couple of days back while working on an ASP.Net 2.0 web site.

I spent several hours barking up the wrong code tree since I was convinced it had to do with some recent code changes I made.

But as it turns out this problem is as old as the server itself and for some reason has not been fixed by any .Net patches.

The jist of it is that if you encounter .net exceptions that only happen on your server with certain types of traffic ( examples: google bot, yahoo bot and some other esteemed visitors), you might be the victim of an annoying bug that has existed, as far as I could tell, for a couple of years and has not been fixed till date.

The telltale signs would be server exceptions that look like ->

Exception of type 'System.Web.HttpUnhandledException' was thrown.
Stack trace: at System.Web.UI.Page.HandleError(Exception e)

And inner exception type ->

System.Web.HttpException: Cannot use a leading .. to exit above the top directory. at System.Web.Util.UrlPath.ReduceVirtualPath(String path)

---------------

As it turns out this bug has to do with .Net 2.0 browser detection bug and can be fixed by adding a browser definition file to correct the problem.

You can also reproduce and test the browser detection bug here.

Note that this bug often occurs when you use url rewriting on your server.

I was really surprised to discover this bug a couple of days back while working on an ASP.Net 2.0 web site.

I spent several hours barking up the wrong code tree since I was convinced it had to do with some recent code changes I made.

But as it turns out this problem is as old as the server itself and for some reason has not been fixed by any .Net patches.

The jist of it is that if you encounter .net exceptions that only happen on your server with certain types of traffic ( examples: google bot, yahoo bot and some other esteemed visitors), you might be the victim of an annoying bug that has existed, as far as I could tell, for a couple of years and has not been fixed till date.

The telltale signs would be server exceptions that look like ->

Exception of type 'System.Web.HttpUnhandledException' was thrown.
Stack trace: at System.Web.UI.Page.HandleError(Exception e)

And inner exception type ->

System.Web.HttpException: Cannot use a leading .. to exit above the top directory. at System.Web.Util.UrlPath.ReduceVirtualPath(String path)

---------------

As it turns out this bug has to do with .Net 2.0 browser detection bug and can be fixed by adding a browser definition file to correct the problem.

You can also reproduce and test the browser detection bug here.

Note that this bug often occurs when you use url rewriting on your server.

If you receive the following error:  Could not download the Silverlight application. Check web server settings.

The problem might be the fact that the .xap mime type is not registered on the IIS server you are using.

If you have control over your server then you can just register the missing mime type.

If you are not that lucky you might need to find a workaround like the one below.

The idea is based on an older solution for Silverlight 1.0 and xaml files.

Since the problem is do to the fact that xap is not a registered mime type, we can cheat a little by creating an http handler that will handle requests for xap files.

The http handler will deliver the content of the xap file using a mime type that is known to the server. 

Since a xap file is actually a zip file we can use that mime type as the delivery content type.

Example:

Create a new class file called HttpXapHandler.cs.

Copy the following code to the file and add the file to your App_Code directory.

public class HttpXapHandler : IHttpHandler

After you created the http handler add the following line to your web.config file inside the httpHandlers section(note the bold part):

Now that we have an http xap handler our web site should be able to accept requests like this:

http://www.MySiteNameGoesHere.com/getXapFile.ashx?fileName=Silverlight2.xap

To actually use this inside a web page take a look at the next example.

Usage example:

To access the .xap files in your web pages you will need to replace each occurrence of the source=[xap file name] with source=getXapFile.ashx?fileName=[xap file name].

In your html page this will look something like the following (note the bold part):

good luck!

If you receive the following error:  Could not download the Silverlight application. Check web server settings.

The problem might be the fact that the .xap mime type is not registered on the IIS server you are using.

If you have control over your server then you can just register the missing mime type.

If you are not that lucky you might need to find a workaround like the one below.

The idea is based on an older solution for Silverlight 1.0 and xaml files.

Since the problem is do to the fact that xap is not a registered mime type, we can cheat a little by creating an http handler that will handle requests for xap files.

The http handler will deliver the content of the xap file using a mime type that is known to the server. 

Since a xap file is actually a zip file we can use that mime type as the delivery content type.

Example:

Create a new class file called HttpXapHandler.cs.

Copy the following code to the file and add the file to your App_Code directory.

public class HttpXapHandler : IHttpHandler

After you created the http handler add the following line to your web.config file inside the httpHandlers section(note the bold part):

Now that we have an http xap handler our web site should be able to accept requests like this:

http://www.MySiteNameGoesHere.com/getXapFile.ashx?fileName=Silverlight2.xap

To actually use this inside a web page take a look at the next example.

Usage example:

To access the .xap files in your web pages you will need to replace each occurrence of the source=[xap file name] with source=getXapFile.ashx?fileName=[xap file name].

In your html page this will look something like the following (note the bold part):

good luck!

If you receive the following error:  Could not download the Silverlight application. Check web server settings.

The problem might be the fact that the .xap mime type is not registered on the IIS server you are using.

If you have control over your server then you can just register the missing mime type.

If you are not that lucky you might need to find a workaround like the one below.

The idea is based on an older solution for Silverlight 1.0 and xaml files.

Since the problem is do to the fact that xap is not a registered mime type, we can cheat a little by creating an http handler that will handle requests for xap files.

The http handler will deliver the content of the xap file using a mime type that is known to the server. 

Since a xap file is actually a zip file we can use that mime type as the delivery content type.

Example:

Create a new class file called HttpXapHandler.cs.

Copy the following code to the file and add the file to your App_Code directory.

public class HttpXapHandler : IHttpHandler

After you created the http handler add the following line to your web.config file inside the httpHandlers section(note the bold part):

Now that we have an http xap handler our web site should be able to accept requests like this:

http://www.MySiteNameGoesHere.com/getXapFile.ashx?fileName=Silverlight2.xap

To actually use this inside a web page take a look at the next example.

Usage example:

To access the .xap files in your web pages you will need to replace each occurrence of the source=[xap file name] with source=getXapFile.ashx?fileName=[xap file name].

In your html page this will look something like the following (note the bold part):

good luck!

If you receive the following error:  Could not download the Silverlight application. Check web server settings.

The problem might be the fact that the .xap mime type is not registered on the IIS server you are using.

If you have control over your server then you can just register the missing mime type.

If you are not that lucky you might need to find a workaround like the one below.

The idea is based on an older solution for Silverlight 1.0 and xaml files.

Since the problem is do to the fact that xap is not a registered mime type, we can cheat a little by creating an http handler that will handle requests for xap files.

The http handler will deliver the content of the xap file using a mime type that is known to the server. 

Since a xap file is actually a zip file we can use that mime type as the delivery content type.

Example:

Create a new class file called HttpXapHandler.cs.

Copy the following code to the file and add the file to your App_Code directory.

public class HttpXapHandler : IHttpHandler

After you created the http handler add the following line to your web.config file inside the httpHandlers section(note the bold part):

Now that we have an http xap handler our web site should be able to accept requests like this:

http://www.MySiteNameGoesHere.com/getXapFile.ashx?fileName=Silverlight2.xap

To actually use this inside a web page take a look at the next example.

Usage example:

To access the .xap files in your web pages you will need to replace each occurrence of the source=[xap file name] with source=getXapFile.ashx?fileName=[xap file name].

In your html page this will look something like the following (note the bold part):

good luck!

If you receive the following error:  Could not download the Silverlight application. Check web server settings.

The problem might be the fact that the .xap mime type is not registered on the IIS server you are using.

If you have control over your server then you can just register the missing mime type.

If you are not that lucky you might need to find a workaround like the one below.

The idea is based on an older solution for Silverlight 1.0 and xaml files.

Since the problem is do to the fact that xap is not a registered mime type, we can cheat a little by creating an http handler that will handle requests for xap files.

The http handler will deliver the content of the xap file using a mime type that is known to the server. 

Since a xap file is actually a zip file we can use that mime type as the delivery content type.

Example:

Create a new class file called HttpXapHandler.cs.

Copy the following code to the file and add the file to your App_Code directory.

public class HttpXapHandler : IHttpHandler

After you created the http handler add the following line to your web.config file inside the httpHandlers section(note the bold part):

Now that we have an http xap handler our web site should be able to accept requests like this:

http://www.MySiteNameGoesHere.com/getXapFile.ashx?fileName=Silverlight2.xap

To actually use this inside a web page take a look at the next example.

Usage example:

To access the .xap files in your web pages you will need to replace each occurrence of the source=[xap file name] with source=getXapFile.ashx?fileName=[xap file name].

In your html page this will look something like the following (note the bold part):

good luck!

If you receive the following error:  Could not download the Silverlight application. Check web server settings.

The problem might be the fact that the .xap mime type is not registered on the IIS server you are using.

If you have control over your server then you can just register the missing mime type.

If you are not that lucky you might need to find a workaround like the one below.

The idea is based on an older solution for Silverlight 1.0 and xaml files.

Since the problem is do to the fact that xap is not a registered mime type, we can cheat a little by creating an http handler that will handle requests for xap files.

The http handler will deliver the content of the xap file using a mime type that is known to the server. 

Since a xap file is actually a zip file we can use that mime type as the delivery content type.

Example:

Create a new class file called HttpXapHandler.cs.

Copy the following code to the file and add the file to your App_Code directory.

public class HttpXapHandler : IHttpHandler

After you created the http handler add the following line to your web.config file inside the httpHandlers section(note the bold part):

Now that we have an http xap handler our web site should be able to accept requests like this:

http://www.MySiteNameGoesHere.com/getXapFile.ashx?fileName=Silverlight2.xap

To actually use this inside a web page take a look at the next example.

Usage example:

To access the .xap files in your web pages you will need to replace each occurrence of the source=[xap file name] with source=getXapFile.ashx?fileName=[xap file name].

In your html page this will look something like the following (note the bold part):

good luck!

If you receive the following error:  Could not download the Silverlight application. Check web server settings.

The problem might be the fact that the .xap mime type is not registered on the IIS server you are using.

If you have control over your server then you can just register the missing mime type.

If you are not that lucky you might need to find a workaround like the one below.

The idea is based on an older solution for Silverlight 1.0 and xaml files.

Since the problem is do to the fact that xap is not a registered mime type, we can cheat a little by creating an http handler that will handle requests for xap files.

The http handler will deliver the content of the xap file using a mime type that is known to the server. 

Since a xap file is actually a zip file we can use that mime type as the delivery content type.

Example:

Create a new class file called HttpXapHandler.cs.

Copy the following code to the file and add the file to your App_Code directory.

public class HttpXapHandler : IHttpHandler

After you created the http handler add the following line to your web.config file inside the httpHandlers section(note the bold part):

Now that we have an http xap handler our web site should be able to accept requests like this:

http://www.MySiteNameGoesHere.com/getXapFile.ashx?fileName=Silverlight2.xap

To actually use this inside a web page take a look at the next example.

Usage example:

To access the .xap files in your web pages you will need to replace each occurrence of the source=[xap file name] with source=getXapFile.ashx?fileName=[xap file name].

In your html page this will look something like the following (note the bold part):

good luck!

If you receive the following error:  Could not download the Silverlight application. Check web server settings.

The problem might be the fact that the .xap mime type is not registered on the IIS server you are using.

If you have control over your server then you can just register the missing mime type.

If you are not that lucky you might need to find a workaround like the one below.

The idea is based on an older solution for Silverlight 1.0 and xaml files.

Since the problem is do to the fact that xap is not a registered mime type, we can cheat a little by creating an http handler that will handle requests for xap files.

The http handler will deliver the content of the xap file using a mime type that is known to the server. 

Since a xap file is actually a zip file we can use that mime type as the delivery content type.

Example:

Create a new class file called HttpXapHandler.cs.

Copy the following code to the file and add the file to your App_Code directory.

public class HttpXapHandler : IHttpHandler

After you created the http handler add the following line to your web.config file inside the httpHandlers section(note the bold part):

Now that we have an http xap handler our web site should be able to accept requests like this:

http://www.MySiteNameGoesHere.com/getXapFile.ashx?fileName=Silverlight2.xap

To actually use this inside a web page take a look at the next example.

Usage example:

To access the .xap files in your web pages you will need to replace each occurrence of the source=[xap file name] with source=getXapFile.ashx?fileName=[xap file name].

In your html page this will look something like the following (note the bold part):

good luck!