BadImageFormat Exception at Microsoft.CSharp library

Question

I'm having little problem running my C# application after switching to Windows 8.1 from 8. The problem is that I get this exception from title and there's not much help online. I tried to pinpoint the problem and it seems like my x64 application is trying to call x86 CSharp library. The reference in project leads to a DLL file, that upon calling x64 dumpbin program with /headers parameter outputs:

Dump of file Microsoft.CSharp.dll

PE signature found

File Type: DLL

FILE HEADER VALUES
             14C machine (x86)
               3 number of sections
        4FFA5C64 time date stamp Mon Jul 09 06:21:56 2012
               0 file pointer to symbol table
               0 number of symbols
              E0 size of optional header
            2022 characteristics
                   Executable
                   Application can handle large (>2GB) addresses
                   DLL

Notice the machine is x86, while the application is running in x64 (checked with Environment.Is64BitProcess). This might be the problem I'm facing, however I can't find way to solve it - there seems to be no x64 .Net libraries installed. The only ones I have found are at: C:\\Program Files (x86)\\Reference Assemblies\\Microsoft\\Framework\\.NETFramework . Or maybe I'm completely off and there's some other problem. Anyway the exception occurs at startup in one of constructors and full detail is:

Microsoft.CSharp, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
"Could not load file or assembly 'Microsoft.CSharp, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The module was expected to contain an assembly manifest."

Edit:

While still panicking, I solved this by downloading CSharp.dll and replacing the dummy 0-byte file in path shown in answer by it.

Answer 1

The module was expected to contain an assembly manifest

You've been looking at a reference assembly, it is not the one that's actually loaded when you run your program. Microsoft.CSharp.dll is stored in the GAC, put there by the .NET installer. You can see the file by navigating to c:\\windows\\microsoft.net\\assembly\\gac_msil\\microsoft.csharp. Keep clicking until you get to the file.

The exception message is a very unhealthy one, it doesn't recognize the DLL as a .NET assembly. There are few decent explanations for that, other than the file being corrupted. File corruption is always bad news, a strong hint that your hard-disk is failing. You'll need to get it fixed, follow-up if necessary at superuser.com