I've isolated the issue to the following code. Even the conditions work fine, but when I try to reference previous temperatures, Fluent crashes. I've checked the documentation a few times now, and I'm still not sure why this wouldn't be allowed. Any suggestions? (edit: spelling)
if ((step > 2) && (THREAD_ID(thread)==4))//powder layer @ timestep 3 and beyond

real temp_m1 = C_T_M1(cell,thread); //get previous temperature from FLUENT

real temp_m2 = C_T_M2(cell,thread); //get temperature before previous from FLUENT