Seg fault when accessing cell face velocities F_U, F_V, F_W
 

I am trying to access the F_U, ..., face velocities within the c_face_loop celll looping macro. My udf compiles without errors but returns a seg fault at runtime. The problem is coming from trying to access the cell face velocities. It has me stomped because the face thread pointer is properly assigned, and a similar access to the F_FLUX macro yields no errors. I have shown the problematic segment of this code:

Thread *fthread, *CellThread; face_t face; int n; Domain *domain; cell_t cell = (obtained from another part of the code);
domain = Get_Domain(1);
CellThread = domain->c;

c_face_loop(cell,CellThread,n)
{
face = C_FACE(cell,CellThread,n); fthread = C_FACE_THREAD(cell,CellThread,n);
VmF[0] += CVm*DT*F_FLUX(face,fthread)*F_U(face,fthread)/RhoF/CellVolume;
VmF[1] += CVm*DT*F_FLUX(face,fthread)*F_V(face,fthread)/RhoF/CellVolume;
VmF[2] += CVm*DT*F_FLUX(face,fthread)*F_W(face,fthread)/RhoF/CellVolume;
}

It gives no runtime errors when I remove the F_U, F_V, F_W macros but leave the F_FLUX. Any help would be appreciated.