>>>I downloaded the other project, which I think uses the same thing:
>>>
>>>

>>>EXTERN_C LPCTSTR Invoke1	(LPCTSTR szIn)
>>>{
>>>	AFX_MANAGE_STATE(AfxGetStaticModuleState());
>>>	theApp.ProcessCall(CString(szIn), theApp.m_csRet);
>>>	return theApp.m_csRet;
>>>}

>>>
>>
>>The code I gave earlier should work for this signature. LPCTSTR should automatically map to the string type.
>>
>>Is it possible your code is set to compile for 64 bit (or the platform target is set to Any CPU) but the DLL you're calling is 32-bit? Not sure what the behavior would be in that case.
>
>That may be the problem. I know that dll is set for 32-bit and I have Any CPU for all 3 projects in that solution.
>
>Do you suggest to change this to match?

Yes.