Jim,

When a workbook is shared, it means more than one person can open it for
update.  This is normally disallowed in a multi-user environment.  They both
start with the same copy, and each makes his own edits.  When there's a
conflict, it's between one user who has saved the workbook, and another who
is attempting a save.  The conflict relates to cell(s) that have been
changed by both users.  Remember that they both opened the same original
workbook.  Sharing doesn't give one "master" person control over this.  It
lets each user decide whether to allow his changes to prevail, or the
earlier user who's already saved the workbook.