remove read only - not showing up in properties
 

I am working with a network server. One person created an excel sheet that
is to be added to by others. She did NOT create it as read only. However,
when SOME people open and save they are told it's read only, yet a small
number of others can open and save with NO problem. When I checked the
properties it is not showing up as read only and when I right click the file
name in explorer and click the general tab there is is not showing as read
only. HELP