Tracking down BadImageFormatException in C#

I know It’s been quite some time since my last post, but what can I say? I’ve been quite busy 🙂 Here is the latest issue that I got stuck on for a few hours, and I thought I’d share what worked in the end.

I was working on a large C# project that had a lot of dependencies on native C++ DLLs in Visual Studio 2015. I had compiled all the 3rdparty dependencies to DLLs myself and had included them in the C# project. On my main development machine, everything was working fine, but I couldn’t get the project to work on another machine with a clean Windows 10 install. The project would compile fine but would fail to run with BadImageFormatException.

From prior experience, I knew this error had to do with a mismatch between dependency architectures somewhere (e.g. 32 bit binary is trying to load a 64 bit binary or vice versa). However, this time I was so sure that wasn’t the case because I had built almost all the DLL dependencies myself and I knew that everything was built in x64 mode. Also, it was working fine on my development machine.

After a few hours of frustration and using the Fuslogvw.exe tool without obtaining much more insight about the problem, I decided to use Dependency Walker to see what’s happening. This great little tool did magic! I noticed that one of the dependencies that I hadn’t built myself was actually a 32-bit binary. The reason this was not causing an issue on my development machine was that as bad luck would have it, the 64-bit version of that dependency was in my PATH variable on that machine, so my C# project would load up the correct DLL. However, on other machines with a clean Windows installation, this wasn’t the case and because the only found binary was the 32-bit version, I would receive that dreaded BadImageFormatException.