Unable to load DLL error when the DLL exists in the proper directory.

I'm currently running into an issue loading a DLL from a C++ project located within the same solution (i.e. I have access to the source):

System.DllNotFoundException: 'Unable to load DLL 'mydll.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)'

I've checked my build output directory and 'mydll.dll' definitely exists alongside the .exe file generated by Visual Studio. For some reason I only encounter this issue when I try to run my program in Debug mode - it works perfectly fine in Release mode. I've run the 'mydll.dll' generated from both Debug and Release through Depends (dependency walker) and they both seem identical.

Has anyone experienced this same error when the DLL clearly should be found?