"unexpected file lock by . " error
 

I have an excel spreadsheet that is shared and accessed by 5 computers. Only
one person at a time can make changes. However, periodically I am getting an
"Unexpected file lock by . ........" It states that I can click yes to
unlock and be able to save changes or click NO but be able to SAVE AS a
different file name. This does not happen all the time and I really can't
duplicate it at will. It has appeared on at least two different computers
(not the computer that the file resides on). But it has come up several
times in the last week.

Any suggestions as to why this is happening and what can be done to fix it?

Thanks!!!!