the following error recurs every time i startup & login on the iMac:
There was a problem with Messages. You need to quit and open Messages again.
if i do what it says, Quit & Open again, Messages will then sign-in normally, but the error recurs when i shutdown‑restart the machine.
iMac, OS X Mountain Lion
If you have Messages in your User Login Items, try removing it. Before shutting down, make sure you quit the Messages application.
Messages is not configured to Open at Login; however, the system is set to Reopen windows when logging back in (see screencap), which is likely the source of the problem, b/c that feature is bug-ridden to begin with.
Uncheck the box and see if Messages opens.
Send Apple feedback. They won't answer, but at least will know there is a problem. If enough people send feedback, it may get the problem solved sooner.
An internal Messages error occurred
