Is your Perl script segfaulting, or the program it starts? If it's the external program, we probably can't help you at all.

Also this looks very suspicious to me:

$command= "cfi -N $bsc -1 \"RLSTP:CELL=$cell;\" |" or warn "Cant acces
+s to BSC $bsc\n";
open CFI, $command;
[download]

The string $command will never be false, so the warn is never executed. Likely you want to check the return value of open, though. And you should also check the return value from close, because that's where you can learn about the exit status of the external program (if I remember correctly).