Error while archiving folder "inbox" in store "mailbox - user name".

If you get the error message in the title of this post (with no other information such as 'Access Denied') then most likely your problem is a corrupted OST. I have found that turning off Cached Mode fixes the issue, but that is only a temporary fix. The true fix is to delete the OST file located at %userprofile%\local settings\application data\outlook\ (WinXP) or %userprofile%\appdata\local\microsoft\oulook (Vista) and then reopen Outlook so it rebuilds the OST.