Could not load file or assembly … An attempt was made to load a program with an incorrect format (System.BadImageFormatException)

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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?

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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.

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