Build error - physicsBullet.cpp, ContactAddedCallback

I have been working on compiling Bullet, gMK & Guidebot, have gotten through to the end of GMK/Bullet and got stuck with this:

error C2440: '=' : cannot convert from 'bool (__cdecl *)(btManifoldPoint &,const btCollisionObject *,int,int,const btCollisionObject *,int,int)' to 'ContactAddedCallback' c:torquetorque 3d 1.2enginesourcet3dlogickingmechanicsphysicsbulletphysicsbullet.cpp 43

1> physicsBullet.cpp
1>c:torquetorque 3d 1.2enginesourcet3dlogickingmechanicsphysicsbulletphysicsbullet.cpp(43): error C2440: '=' : cannot convert from 'bool (__cdecl *)(btManifoldPoint &,const btCollisionObject *,int,int,const btCollisionObject *,int,int)' to 'ContactAddedCallback'
1> This conversion requires a reinterpret_cast, a C-style cast or function-style cast



btManifoldResult.cpp & btManifoldResult.h are the associated files, but nothing seems out of place.

Closest rational answer I could find is: It should be a static or global function. Class member function expects to receive an additional hidden parameter called this, so the signature doesn't match.

Here's the line that is causing the error:

gContactAddedCallback = PhysicsBullet::contactAddedCallback;

Any help would be greatly appreciated.