Outlook 2007 "0x8004210e Your mailbox is temporarily unavailable ..." Error

Over the last couple of weeks the majority of times I use Outlook to retrieve my email I receive this error.  The reason I’m bringing this here for help is not only are there some pretty smart people here that may be able to help but there are also some messages I’ve found on the Internet that indicate my NIS 2010 MAY be part of the problem.  I have Charter and I occasional use their WEB interface to access my email and I also retrieve my email on my iPhone and neither of the later two clients have an issue.  Any suggestions for a remedy will definitely be appreciated.