Microsoft Office tracks those locks using files that are created in the same directory as the original file. The document
Somedoc.docx gets a temporary lock file (Microsoft calls it an "owner file"):
~$Somedoc.docx. The same goes for Powerpoint and Excel. The owner of that file is the owner reported in the dialog.
The easiest way out is to delete that file. It is a hidden file, so you should set your Windows Explorer to view "protected operating system files":
- Open Folder Options by clicking the Start button, clicking Control Panel, click Appearance and Personalization, and then click Folder Options.
- Click the View tab.
- Under Advanced settings, click Show hidden files, folders, and drives,
Hide protected operating system files (Recommended), and then click OK.
You should see that file in the same directory the original file is in. Delete it and open the document again.
This situation is explained more elaborately here.