Hi,
After look at the client's feedback and I've got understood the problem that why is redirect to "Page Not Found" because page 'contact' isn't real existing on live. But then you were changed URL to 'contactus' page after login it will take you to the Contact Us page, that's all right!, because there are rewriting rules to force redirect to the real existing page, pcat, icat etc.
However, they want to take the customer to the home page. Would I suggestion to change the URL with home page like this:
http://topsourceportal.com/page/home?tmpgrp=golbon&assignusgrref=golbon&log=2
After login it will take them to the home page. Could you please confirm?