Hello aP00rv, and welcome to Seven Forums. Q1)
These links below may be able to help with this activation error.
(Method F) Error message when you try to activate Windows Vista: "An error has occurred"
and Let me google that for you Q2)
It depends on what type of Windows 7 you will have. A retail copy can be installed and activated on any computer, but must be uninstalled from any previous computer before installing it on another one. A OEM copy can only be activated on the same computer that Windows 7 was originally installed on, and no other computer. Q3)
Windows 7 beta was a Ultimate edition and not a Professional eddition.
Hope this helps,