Having same issue with my N900 that just arrived. I immediately updated to PR1.2 and Nokia Messaging just won't set up correctly. I enter my user and password and it wants to activate instead of use my existing account. An account is created with no email accounts.

My account status is purchased with device so it's not an account issue. Works perfectly on my Nokia E72 and worked perfectly on the first N900 I trialed using PR1.1.1.