There is a problem in VistaPanel, to be more specific users get a 404 error when try to register a domain.
In my view, this is caused by this line on your script: https://ifastnet.com/portal/domainchecker.php&aff=23782 where it returns:
The requested URL /portal/domainchecker.php&aff=23782 was not found on this server.
Maybe you should do it Shopping Cart - IFastnet, I am not sure if that will work.
If anyone wants to test it, just go ahead, it is not going to ruin anything!