invalid argument--why?

wanghong

my code of energy source is following:

#include "udf.h"

#define CON 1850.0

real m[ND_ND];

DEFINE_SOURCE(energy_source, c, t, dS, eqn)

{

real source,r,r0,CON1,volume;

C_VOLUME(c,t);

volume += C_V(c, t);

CON1=CON/volume;

r=sqrt(m[0]*m[0]+m[1]*m[1]);

begin_c_loop(c, t)

{

r0=5.0e-4+4.0e-2*m[2];

if (r0<=r&&-2.5e-3<=m[2]<=0.)

{source=CON1*exp(-(m[0]*m[0]+m[1]*m[1])/r0*r0);

dS[eqn]=0.;

}

else

source=0.;

}

end_c_loop(c, t)

return source;

}

After it is Interpreted and linked to energy source, FLUENT appears following information: Error: GENERAL-CAR-CDR: invalid argument [1]: improper list Error Object: #f. why ?