Upgrading trial accounts is a little buggy. If you just add a regular subscription, it leaves the trial account status on your account and you have to talk to customer support to have the trial account status removed before you can place a house etc.
I hear the following works (but have never had to try it):
1) go to the account management site and cancel the account. This turns off trial account status.
2) *then* add a subscription to the account.