"Unexpected internal error" in S-function builder

Hi
when I build a S-function using S-function Builder, everything compiled successfully. but when I run the model it notifies "Unexpected internal error".
I don't know why it occurs and relates to what.
Appreciate any help...

Inputs (type double) :
1. fraction (size: 1x1)
2. u_n (size: 40x1)
3. T (size: 1x1)
4. b30 (size: 31x1)

Output (C Code):

int_T i;
int_T j;
int_T k = (int_T) T;
int_T frac = (int_T) fraction;
real_T u[200] ={0};
 
   frac = -frac;
       if (frac==-1)
         {
           k=k+1;
           frac=2;
          }
        
   for (i=0;i<200;i++)
     {
       u[i] = u_n[i];
     }
            
   for (i=0;i<40;i++)
     {
        for (j=0;j<10;j++)
          {
            v_n[i] = v_n[i]+u[(i-k+160-j)]*b30[(frac+3*j)]+u[i-k+160+j]*b30[3-frac+3*j];
            u[159+i] = v_n[i];
           }
      }