R – How to build MTd projects which use MDd dlls in VS2005

I had the same error message, but none of the answers here solved it for me. So if you Encounter that Problem when creating a DLL Project that uses MFC, it can be resolved by entering the following line:

extern "C" { int _afxForceUSRDLL; } 

to the cpp file where DllMain is defined. Then your own DllMain implementation is used, rather than the one from dllmain.obj.

When we try to use MFC library, we surely will include afx.h directly or indirectly, then MFC(afx.h) tell the linker to find the symbol of __afxForceUSRDLL and put that object which contains __afxForceUSRDLL into the program, so linker searches and puts dllmodule.obj into our program, because __afxForceUSRDLL is defined in dllmodule.cpp.

That’s the common scenario. When we want to use our own DllMain in a mfc dll project, linker complains that there are two DllMain, one in our code, one in Dllmodule.obj.

So we need to tell the linker to add our dllmain.obj for __afxForceUSRDLL. So we need to define __afxForceUSRDLL in our own cpp file where our own DllMain is defined, then the linker will ignore mfc’s dllmodule.obj and see only one DllMain and never complains.

Source: http://social.msdn.microsoft.com/Forums/en-US/0d78aa6b-1e87-4c01-a4a7-691335b7351a/how-to-build-mfc-application-dll-in-visual-c-2010

You could build your project to link against the release CRT and enable debug information for your code. In "Project Properties" go to C++/General and change the Debug Information Format. In the "Optimization" section turn off optimization. Switch to the "Linker/Debugging" section and enable generation of debug info. Make sure to set the program database file (PDB).

At this point your application will emit debugging information for everything in your code and link against the non-debug DLL CRT. This enables you to debug your application in a Release configuration while avoiding the problems associated with using multiple CRTs in the same application.