I’m sure you already know about this fix for ASP.NET which fixes an issue of “not a valid path” exception, and this fix for ASP.NET 1.1 for the same reason. If you receive this error now on your application, you might not need to apply the hotfix because your ASP.NET version might be higher than the one available with this hotfix, so verify the DLL versions before even requesting the hotfix from Microsoft.
So, after installing the hotfix, you should do the below registry changes (not sure if the hotfix does this automatically – I haven’t tested this):
DWORD HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ASP.NET\VerificationCompatibility = 1
as mentioned in the KB article 932552. But, you might see that this doesn’t work if you run the application pool under 32-bit mode on a x64 Windows Server 2003 or 2008. That’s just because, the ASP.NET reads this key from a different location as below:
DWORD HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\ASP.NET\VerificationCompatibility = 1
I’m sure you doesn’t want me to explain why ASP.NET reads from this location instead of above. If you want, please drop a note.
In IIS 7.0, you would get the below error message while running under Integrated mode:
“HTTP Error 400.0 - Bad Request
ASP.NET detected invalid characters in the URL”
Hope this helps!