# usual syntax
chmod 755, $old or die "Can't chmod $old because: $!\n";

# or using the syntax you have and skipping the 
# useless $cnt temporary variable
if (chmod 0755, $old) {
    print "changed file permissions for $old<BR>";
}
else {
    print "cannot change file perms for $old<BR>System says $!<BR>";
}