Why can't I connect an unmanaged dll?

Question

C++ / C#

I'll give you a simple example.
There is the following C++ library:

And there is a C# code that uses it:

And here the magic begins:
When the C++ library is compiled with VC++, everything works fine, but through TDM-GCC it throws an exception (on the screenshot).
But when I change the target platform from .NET 4.6.2 to .NET 4.0 in the C# project settings, everything starts working with the library compiled via TDM-GCC.
How can this behavior be explained?
How can I include a TDM-GCC compiled library in a .NET 4.6.2 project?

Answer 1

Look at the bit depth of the library and C# program.
The C# program, if nothing is changed, runs under x64. TDM-GCC most likely compiles for x86.
Link libraries must match the program from which they are called.
Convert everything to x64 or x86.

Answer 2

charset specify ASCII