Hey Dom
Once you enter the URL into the text field, then press the submit button, you will then be able to test it by using the linking code with the sorry.asp page below…
So, after you’ve set the bounce back URL then go to
http://www.blackjackballroom.com/sorry.asp?aff_id=affXXXXX
(enter your aff code in the XXXXX)
It should redirect to the page you entered..
The line ‘You MUST enter the FULL domain including the http:// ‘ is just there so people remember to add that. It’s not an error message 
Let me know how you go
Edit: I just logged into your account and tested it out and it seems to be working