Whenever that "sorry, this sytem is temporarily..." message comes up, one or more errors will be logged to the application event log - posting that info here will help us narrow it downa bit. The version of Unity you're using would be good, too.
The most common error here is the call handler you have mapped to do the transfer has a broken message recipient (on the messages page) or owner (on the profile page). For instance you set it up with an owner or recipient that was then later removed from the system.
running dbWalker can help run problems like this down for all your handlers if necessary, but I'd check this call handler in particular to see if that's the issue at hand.
