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.