I created a shared workbook and today I am unable to open it as it is "in use
by another user" and it is "locked for editing." This shouldn't happen if
it's shared, should it? I can open it as read-only, but that defeats the
purpose of having a shared document. What might make this happen and how can
I fix it?

(The workbook is a basic scheduling tool for staff to type when they leave
the office, why, and when they will be back. I anticipate that most of the
folks will open the file, enter their data, save, and close. Two-four of use
might keep it open off and on throughout the day to track employees
whereabouts. The workbook is saved to a Shared Data folder on our server that
everyone has access to.)