That is a possibility that I can’t easily verify at this time. Now I am thinking: Maybe a reboot was all that was needed in my case which did not necessarily require rebuilding the database. However, rebooting the Mac afterwords did the trick.
At first, this did not work for me (but read on): Outlook 2011 would still refuse to start up (just showing a brief splash screen and then aborting, same as before) even AFTER successfully rebuilding the Outlook database following the instructions here.
