I followed some advice in another thread to try and isolate the issue - 5 or 6 steps ranging from deleting preferences .plist files to selectively removing Office-specific files but none of them positively affected the situation. 

I stumbled across the workaround (to remove all shared calendars) after noticing that Outlook was downloading calendar data from most of the calendars very frequently and repetitively (i.e., I can't imagine changes at the frequency that was occurring).

However - I still need access to these shared calendars - so looking for advise on how to resolve this issue.

Thanks!

Tony.