After installing Visual Studio 2005 I would intermittently get this error: Unable to cast object of type 'ASP.type' to type 'ASP.type' It was only intermittent and though I knew it had something to do with the compilation model I was going crazy until i found the post for the pre-release KB hotfix. I just noticed it has been released officially now at: http://support.microsoft.com/?kbid=915782&SD=tech