Unable to edit .XLS file

I am the owner of a file and when I try to open it I get a message that reads as follows:

File in Use

<filename>.xls is locked for editing

by <user>

Open 'Read-Only" or, click "Notify" to open read-only and recieve notification when the document is no longer in use.


I know the document is NOT in use by me or any other user. Any suggestions????