segmentation error while using mpz_powm in a loop

[shrims . .... ..]

I am getting segmentation fault in the program below.
I have initialised all the GMP variables properly...
But still i am getting segmentation fault at  *mpz_powm( );
*The loop runs only once and second time it gives segmentation fault at
mpz_powm...
*
The code is as follows:

**mpz_t bigbody,encbody,decbody,n,d,e;

mpz_init(bigbody);
mpz_init(decbody);

while(i<noOfBlocks)
{

strncpy(substring, data_buffer + lower, upper);
*(substring+308)='\0';

lower=upper;
upper=upper+308;
i++;


mpz_set_str(bigbody,substring,10);

//size=len;

mpz_powm (decbody, bigbody, d, n);

}


The again i tried to use arrays but this time the loop runs for 2 times and
then gives segmentation fault...

The code is as follows..

mpz_t array[10];
//mpz_array_init (array, 10, 308);
mpz_t array1[10];
//mpz_array_init (array1, 10, 308);

while(i<noOfBlocks)
{
   strncpy(substring, data_buffer + lower, upper);
   lower=upper;
   upper=upper+308;
   mpz_init_set_str(array[i],substring,10);

   mpz_get_str (STR, 10, array[i]);
   strcat(STR,"\0");

    syslog( LOG_INFO, "conn# %d - Encrypted-Biginteger = %s",
cd->connection_num, STR );

    mpz_init(array1[i]);

    mpz_powm (array1[i], array[i], d, n);
}

*
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://gmplib.org/list-archives/gmp-bugs/attachments/20090508/d2903a9a/attachment-0001.html>