C :: MSVS Has Triggered A Breakpoint

how to implement calloc, malloc and free. At the end of my program, I keep getting a "windows has triggered a break point" error. Im pretty sure that this error is happening because of the way I am implementing free because this is the error I am getting in free.c - " retval = HeapFree(_crtheap, 0, pBlock);".here is the code which I allocate and free memory:

Code:

int main (){
WORDS userWords[16];
char **board;
int i=0, n=0, numWords=0;
srand(time(NULL));
numWords = enterWords(userWords);
}

[code]....