'declaration1' : function differs from 'declaration2' only by return type or calling convention
A specialization of a function template differs from the primary function template in return type or calling convention.
The following code will generate this error:
template<class T> void __cdecl f(T);
template<> void __stdcall f(int);
Note This error is active only when the /Za compiler optioin (Disable Language Extensions) is specified.