Build dll failed (_DLLMain@12 already defined), but why?

Summary: My attempt to build a procedure dll failed with error LNK2005 : _DLLMain@12 already defined.

Process: I am trying to build a procedure dll using VC++ 2003. I created the project from the Extended Stored Procedure template. This template compiles OK. I replaced #include <windows.h> with #include <afxcoll.h> in stdafx.h because I need to use the collection classes in the functions. Build this project again and get the error messages:

------ Build started: Project: testdll3, Configuration: Release Win32 ------

Compiling...
stdafx.cpp
 WINVER not defined. Defaulting to 0x0501 (Windows XP and Windows .NET Server)
Compiling...
proc.cpp
testdll3.cpp
Generating Code...
Linking...
nafxcw.lib(dllmodul.obj) : error LNK2005: _DllMain@12 already defined in testdll3.obj
nafxcw.lib(dllmodul.obj) : warning LNK4006: _DllMain@12 already defined in testdll3.obj; second definition ignored

Release/testdll3.dll : fatal error LNK1120: 3 unresolved externals

---------------------- Done ----------------------

By the way, using afxtempl.h instead of afxcoll.h would give the same result. I searched MSDN library and found a few leads to the problem, but none of them apply to this situation.

Can anyone help me

Thanks.
xzhutiger