Hi,
Once the Apple ID have been "registered" and is listed in the iMessages account pane in the Messages Preferences it should not need to be entered again.
However there is a sort of "known issue" with Messages reaching version 7.0.1 with the OS X 10.8.2 update that needs the Mac's Serial Number to be present (It is normally read in System Information or in the About this Mac pane (click the current OS line twice).
8:33 PM Saturday; January 5, 2013
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously