So I figured it out - there must have been some change from previous versions, because logging in as user.name@domain.com always worked, then after a recent SM upgrade it would say "User not found".  The solution was to login  as user.name WITHOUT the @domain being specified.  Note that the field on the Web UI asks to login with the "Email Address" and this is inconsistent with what actually works in this case.  Other users can login with or without the domain specified and this problem seems to be associated only with the first user ever created on this deployment.

Hope this helps someone else.  Thx.