I always get the below exception if I make a configuration change to the web.config file then request a page without re-building the project.

Exception:

Unable to cast object of type 'System.Web.Compilation.BuildResultCompiledAssembly' to type 'System.Web.Compilation.BuildResultCompiledGlobalAsaxType'.

Stack Trace:

[InvalidCastException]: Unable to cast object of type 'System.Web.Compilation.BuildResultCompiledAssembly' to type 'System.Web.Compilation.BuildResultCompiledGlobalAsaxType'.
   at System.Web.Compilation.ApplicationBuildProvider.GetGlobalAsaxBuildResult(Boolean isPrecompiledApp)
   at System.Web.Compilation.BuildManager.CompileGlobalAsax()
   at System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled()
[HttpException]: Unable to cast object of type 'System.Web.Compilation.BuildResultCompiledAssembly' to type 'System.Web.Compilation.BuildResultCompiledGlobalAsaxType'.
   at System.Web.Compilation.BuildManager.ReportTopLevelCompilationException()
   at System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled()
   at System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters)
[HttpException]: Unable to cast object of type 'System.Web.Compilation.BuildResultCompiledAssembly' to type 'System.Web.Compilation.BuildResultCompiledGlobalAsaxType'.
   at System.Web.HttpRuntime.FirstRequestInit(HttpContext context)
   at System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context)
   at System.Web.HttpRuntime.ProcessRequestInternal(HttpWorkerRequest wr)

I have now backed out the project from WAP as it requires frequent web.config amendments and appears not to be stable with a global.asax file.

Change to a neutral assembly in AssemblyInfo.cs

[assembly: AssemblyCulture("")]

see further: http://support.microsoft.com/kb/924731

or http://yurykorolev.blogspot.com/2007/10/localization-errors-in-aspnet.html