0x80040102 - Outlook 2010 - Sharepoint calendar error in Outlook 2010

Having read through all the articles there is no definitive answer for this problem.

Error: Task 'SharePoint' reported error (0x80040102) : 'Outlook cannot connect to the SharePoint List (<calendar-name>). The server may not be reachable from your location. Contact the SharePoint site administrator for more information.  HTTP 0.'

• Outlook 2010 running on XP and W7
• SBS 2012 on server

Everyone running Outlook 2007 or below is absolutely fine. Both internally and externally.

I would be very grateful if someone could either:

1) Provide a resolution to this error.  All articles i am reading, even ones assigned as solutions, provide no insight as to the root cause and a clear resolution.

2) Admit to an issue within Outlook 2010 and advise on possibility of future solution.

I look forward to any insight on this.  Let's be careful out there ;-)

Steve Welsh