“An attempt was made to load a program with an incorrect format” even when the platforms are the same

Question

I\'m calling functions from a 32-bit unmanaged DLL on a 64-bit system. What I get is:

BadImageFormatException: An attempt was made to load a program w

Answer 1

With Visual Studio 2019 I had a similar issue when I wanted to run tests (MSTest directly from VS). In my case I only had an x64 native DLL and I received this error message. First, I thought it is because Visual Studio runs as x86 but this page helped me to solve the issue:

Run unit test as a 64-bit process

It says

1. Set your projects to Any CPU
2. Explicitly define processor architecture

I did both (I explicitly set x64) and then my tests started to work.

Answer 2

Somehow, the Build checkbox in the Configuration Manager had been unchecked for my executable, so it was still running with the old Any CPU build. After I fixed that, Visual Studio complained that it couldn't debug the assembly, but that was fixed with a restart.

Answer 3

In my case it was wrong content of the file. DLL was downloaded from the web, but content of the DLL was HTML page :D Try to check if it is binary file, if it seems like correct DLL :)

Answer 4

I was able to fix this issue by matching my build version to the .NET version on the server.

I double clicked the .exe just to see what would happen and it told me to install 4.5....

So I downgraded to 4.0 and it worked!

So make sure your versions match. It ran on my dev box fine, but server had older .NET version.

Answer 5

In my case I was using a native DLL in C#. This DLL depended on couple of other DLLs that were missing. Once those other DLLs were added everything worked.

Answer 6

If you are using Any CPU, you might encounter this issue if the Prefer 32-bit option is checked:

Make sure you uncheck this option in the project's property's Build tab!