How to use a C++ dll in Unity3D?

Question

I am aware of this similar question, but it does not respond to my problem.

I have written two .dlls using Visual Studio 2010. One is in C++, and communicat

Answer 1

This also happens when Unity can find your DLL, but is not able to find it's dependencies. Obvious fix is to place dependency DLLs into /Plugins as well, or link your dependencies statically.

Less obvious reason is when your DLL depends on Visual Studio runtime library dynamically, i.e. is built with Properties -> C/C++ -> Code Generation -> /MD option. Change it to /MT to link with runtime statically.