Link error on changing from platform toolset to v100 to v120

I have a piece of code that was building perfectly fine until I changed my platform toolset to Visual Studio (v120). I am using MSVC to build a 64bit DLL. Has anybody else seen or come across these error messages while trying to do the same?? These are the error messages that I get.

error LNK2005: "void __cdecl std::_Enable_shared(void const volatile *,void const volatile *)" (?_Enable_shared@std@@YAXPEDX0@Z) already defined in ACG.obj

error LNK2005: "void __cdecl std::declare_reachable(void *)" (?declare_reachable@std@@YAXPEAX@Z) already defined in ACG.obj

error LNK2005: "void __cdecl std::declare_no_pointers(char *,unsigned __int64)" (?declare_no_pointers@std@@YAXPEAD_K@Z) already defined in ACG.obj

error LNK2005: "void __cdecl std::undeclare_no_pointers(char *,unsigned __int64)" (?undeclare_no_pointers@std@@YAXPEAD_K@Z) already defined in ACG.obj

error LNK2005: "enum std::pointer_safety __cdecl std::get_pointer_safety(void)" (?get_pointer_safety@std@@YA?AW4pointer_safety@1@XZ) already defined in ACG.obj

error LNK2005: "void * __cdecl std::align(unsigned __int64,unsigned __int64,void * &,unsigned __int64 &)" (?align@std@@YAPEAX_K0AEAPEAXAEA_K@Z) already defined in ACG.obj