How to get gata of previous time step
 

Hi,
I am trying to define a source to a cell zone. The source is a function of temperature of the previous time step. I wrote the UDF as follows:

include "udf.h"
DEFINE_SOURCE(heat_source,c,t,dS,eqn)
{
real x[ND_ND];
real source;
real tem1;
tem1=C_T_M1(c,t);
source=tem1/1000;
dS[eqn]=0.0;
return source;
}


I was able to interpreted or complied the UDF and loaded it and defined to the cell zone. however, when trying to run Fluent, It gave the information:
FLUENT received fatal signal (ACCESS_VIOLATION)

Can anybody help me to solve this problem?

Regards