usr/bin/perl is not the same as /usr/bin/perl
The first is a relative path, so if your script resides in /var/mydir,
it will expect to find perl at /var/mydir/usr/bin/perl
If your script happend to be in the root dir ie. / , then it would
work fine.
Always, always, always use an absolute path, this way if you move your script, it still finds the perl.