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 just had this error message running IIS Express in Visual Studio 2015. In my case I needed to be running the 64 bit version of IIS Express:

Tools -> Options -> Projects and Solutions -> Web Projects
Check the box that says "Use the 64 bit version of IIS Express for web sites and projects".

Screenshot:

Answer 2

It can be a little funny, but I had the same problem with normal working code. I added StreamWriter and StreamReader and it gave that error. The solution was I took that code into comment brackets then did debug and it started to work again

Answer 3

I had this same problem. I had set Project A's "Platform Target" ("Project A"(Right Click)->Properties->Build->"Platform Target") to x86 but kept Project B's at "Any CPU". Setting Project B's to "x86" fixed this.

Answer 4

My machine showed me a BIOS update and I wondered if that has something to do with the sudden popping-up of this error. And after I did the update, the error was resolved and the solution built fine.