[Andy Z]

() tells PHP that show_nopermission is a function. That isn't a standard PHP function, and I don't believe it is defined by vb's functions.php, either. The fatal error is PHP telling you it doesn't understand the function nad can't excute the script. I'm not sure what you should use instead of that function or you can define that function (if you know how) in functions.php. I'm sure someone else can tell you what to replace show_nopermissions() with. You cannot redirect a PHP fatal error to a custom error page.