Can't hadle error

[Lorenzo Caggioni]

Hi!
I write a big program in perl that open some file, and copy them to an other
directory.
To do move files I use this command:

 system("mv","in_file/i","in_file/o") == 0
           or die "Cannot reject input file: $! \n";

At the beginning, when the program aws little, it worked fine: If it can't
find the file it wrote the message "Cannot...."
Now, after adding some new command the program exit with no error message.
What can be appened?

Thanks

Lorenzo