So why did you click on trial?
Re-enter your registration code.. If it won't take your code, Please see this post:
viewtopic.php?f=15&t=13444&view=unread#p63337You could try disabling your firewall temporarily while you register; and if you're on Vista, make sure you are running PT3 as Administrator; but other than that you will have to revert to Build 3 for now.
Once you have it set up as 'Registered' again, you may need to reconnect to your database using Database Management -> New; and enable 'this database exists' then browse to select it.