Could not load file or assembly … An attempt was m

Question

I have two projects, ProjectA and ProjectB. ProjectB is a console application, which depends on ProjectA. Yesterday, everything was working fine, but suddenly today when I run ProjectB I get this:

BadImageFormatException was unhandled:
Could not load file or assembly 'ProjectA, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. An attempt was made to load a program with an incorrect format.

Both are just regular projects, with no dependencies on any other non-.Net projects. Both are fully .Net - there is no native code, and no P/Invoke. I have other projects which depend on ProjectA and still work just fine.

Things I have tried:

• Make sure both projects are set to "Any CPU," with the build checkbox checked. They are.
• Make sure both projects are for the same Target Framework (.Net 4.0 Client Profile).
• Under ProjectB --> References --> ProjectA --> Properties, make sure "Copy Local" is set to "True" _ (I verified that ProjectA.dll is being copied correctly)
• Clean/Rebuild the solution. I even tried manually deleting the /bin and /obj folders in both projects.
• Restart Visual Studio. Restart my computer.
• Check out an entirely new copy of the repository.

But I still get the same error. I have no idea what I did to cause this, nor how to fix it. Any ideas?

Answer 1

I had the same issue with multiple projects in the same solution, i ended up setting all of the target frameworks to .NET Framework 4 and x86 for the target CPU and it finally successfully compiled.

Answer 2

In my project for C#, project property->[Build]->Platform target: Any CPU, and uncheck the Prefer 32-bit to let compiler to choose automatically.

Answer 3

None of these solutions worked for me - but by deleting the contents of bin and obj folders everything was cool again.

Answer 4

I am pretty sure you're having a 32-bit / 64-bit conflict. It sounds like your main project might be set to 32-bit while the class its referencing is set to 64-bit. Try looking at this SO question and this one too. Between the two of them, you should be able to figure out your problem.

Answer 5

You may need to change the Appication Pool setting "Enable 32bit Applications" to TRUE in IIS7 if you have at least 1 32bit dll\exe in your project.

Answer 6

I also had this problem running unit tests by using ReSharper on Visual Studio 2017 and fixed it with following config:

Also you can change the ReSharper's run test setting: https://resharper-support.jetbrains.com/hc/en-us/articles/207242715-How-to-run-MSTest-tests-using-x64-configuration