You must carefully read and understand the error message. Here is "Error looking up function 'GetCompanyCode': The specified procedure could not be found."
So the linker says that dll is found but
the function not. Check with the good olddepedency walker
that the function name is properly exported. My guess is that the __stdcall makes some changes in the so called decorated name.
And I would export an int as result, because it is native data type.