Read Only Excel File
 

I have a 2002 spreadsheet that I have open on my Windows XP machine. I leave
it open all day. Other users may open it for read only purposes. After a
while, when I attempt to save my changes, I am told that it is read only or
in use by someone else. I know that Mac OSX and OS9 as well as Windows XP
users are accessing this file. Why are others able to take control of my
file when I am the one who opened it first?