locked by 'another user'

[jeremy]

When I try and open a shared workbook, from any computer
in our office, I get an error message saying that the file
is "locked for editing by 'another user'." It actually
says "another user" and not just the name of one of the
computers in the network. This file is updated from time
to time, and we are currently unable to do so. Help is
appreciated. Thank you!!

Jeremy