When upgrading from DNN 4.03.07 to 4.05.03 I get an error about various files that are in different languages which need to be compiled together and therefore is not allowed, how can I rectify this problem.

I'll try to give the complete error: It's as follows:

The files, file1.vb and file2.cs are in a different language, which is not allowed since they have to be compiled together.

I'm using file1 and file2 as placeholders since the error occurs for multiple files.

Thanks

I'm having the same problem. Here is the exact error message:

 The files '/App_Code/Global.asax.vb' and '/App_Code/TransactionLog/SqlDataProvider.cs' use a different language, which is not allowed since they need to be compiled together.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: The files '/App_Code/Global.asax.vb' and '/App_Code/TransactionLog/SqlDataProvider.cs' use a different language, which is not allowed since they need to be compiled together.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[HttpException (0x80004005): The files '/App_Code/Global.asax.vb' and '/App_Code/TransactionLog/SqlDataProvider.cs' use a different language, which is not allowed since they need to be compiled together.]
   System.Web.Compilation.BuildProvidersCompiler.ProcessBuildProviders() +957
   System.Web.Compilation.BuildProvidersCompiler.PerformBuild() +29
   System.Web.Compilation.CodeDirectoryCompiler.GetCodeDirectoryAssembly(VirtualPath virtualDir, CodeDirectoryType dirType, String assemblyName, StringSet excludedSubdirectories, Boolean isDirectoryAllowed) +387
   System.Web.Compilation.BuildManager.CompileCodeDirectory(VirtualPath virtualDir, CodeDirectoryType dirType, String assemblyName, StringSet excludedSubdirectories) +125
   System.Web.Compilation.BuildManager.CompileCodeDirectories() +525
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +448

[HttpException (0x80004005): The files '/App_Code/Global.asax.vb' and '/App_Code/TransactionLog/SqlDataProvider.cs' use a different language, which is not allowed since they need to be compiled together.]
   System.Web.Compilation.BuildManager.ReportTopLevelCompilationException() +57
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +612
   System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters) +521

[HttpException (0x80004005): The files '/App_Code/Global.asax.vb' and '/App_Code/TransactionLog/SqlDataProvider.cs' use a different language, which is not allowed since they need to be compiled together.]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +3540923
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +69
   System.Web.HttpRuntime.ProcessRequestInternal(HttpWorkerRequest wr) +275