In case you haven’t seen the Exchange Team’s Blog post on this topic...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.

The fix will be available with the February 2011 Cumulative Update for Office 2007, which will be available later this month. Sorry for any inconvenience this may have caused.