Issue

Trying to open MS Excel file, user gets a File in Use message:

File in Use
<filename> is locked for editing

This would be normal, as the file was really locked, but the username in the message was not of the user who had had the file opened. It was another user on the same network that hasn’t worked on that file for quite some time.

Resolution

The issue was caused by a leftover old temporary MS Excel file the was at some point created by a user whose name was in the locked file message. Deleting the temporary file resolved the issue. To view temporary MS Office files you need to set Windows Explorer to show hidden and system files (Tools > Folder Options > View). They are created in the same folder as the original file, with prefix ~$

Windows 7
Microsoft Excel 2010