Debra Dalgleish has a suggestion that usually works for standalone pc's:
http://contextures.com/xlfaqApp.html#ReadOnly

But if the file is on a network, maybe rebooting that server would help.

Pearl wrote:

have a spreadsheet that is used by many of us. Recently, we all get the
following message: "budget.xls. cannot be accessed. The file may be
read-only, or you may be trying to access a read only location. Or, the
server this document is stored on may not be responding"

I've copied the file to my local hard drive and it still gives me this
message. My fear is someone accidentally setup some security on the file and
did not realize he/she did it or if they did, they won't fess up to it. How
do I remove this security? I'm the administrator of this file and have to
provide access to it for everyone.

--

Dave Peterson