Quick post to inform you that we've found an issue in Exchange 2010 Personal Archives support for Outlook 2007 in the December 2010 Cumulative Update for Office 2007, which may result in users being unable to access their archive mailbox.
Our friends in the Outlook team have been working hard to fix this. The fix has been checked-in in the February 2011 Cumulative Update for Office 2007, which will be available later this month. As with all updates, we recommend that you test them in a non-production environment before deploying them in production. Sorry for any inconvenience this may have caused.