Open up the subbill.ini. Make sure that AllowNewUsers is 1. The SysopPassword can be anything you want, but it is not too great. Only good if you are on the VIE billing (i know all their secrets :P Like their subbill.exe has all the cool stuff like the new "shark" command, which i do know what it is). The BillingPassword should be the same as in the server.ini section [Billing]. The Port should be the same as in the server.ini section [Billing]. That is all you need to to in there.
Step: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.