Failed to load dll error

Hello all,

I created a C++ dll in Visual Studio 2010 which depends on another dll. I have tested this new dll in VS and everything works as expected. I put these files into Unity 5.1.0f3 and the project is able to build. When I try to run it, I get the following error:
Failed to load 'Assets/Plugins/x86_64/myFile.dll' with error 'The operation completed successfully.', GetDllDirectory returned ''. If GetDllDirectory returned non empty path, check that you're using SetDirectoryDll correctly.

It seems Unity can find the file but cannot open/read it. Since it cannot open the file I later receive the DllNotFoundException error.

Some troubleshooting options I have already tried:
-Putting the dependent dll in the base unity.exe folder
-Downloading the 32 and 64 bit VS 2010 and 2013 (just to be safe) Redistributable files
-I am using 64-bit editor with 64-bit dll
-Creating a wrapper for the dll to call from unity script

Does anyone know what I can do to fix this?

Thanks in advance