Straight from Microsoft KB 313472:
This behaviour may occur if Word determines that the owner file for
the document already exists. This may occur if one or more of the
following conditions are true:
- Word previously quit improperly and, therefore, did not delete the owner file.
- A second instance of Word is running in the background with the document already open.
- The document is shared over a network, and another user has it open.
From my personal experience, I've found a combination of the first and
third point above can recreate this error quite constantly.
Temp files, left next to the original file on the network (especially
if the file is large, she copy-pastes a LOT or it is open all day) are the cause.
To resolve this issue, first confirm that another user on the network
does not have the document open. If the document is in use, open the
document as read-only. If it is not in use, quit all instances of
Word, and then remove the owner file. To do so, follow these steps.
NOTE: Because there are several versions of Microsoft Windows, the
following steps may be different on your computer. If they are, see
your product documentation to complete these steps.
- Quit all instances of Word. To do so, follow these steps:
1. Save all your work, and then quit all programs.
2. Press CTRL+ALT+DELETE to open the Windows Security dialog box.
3. Click Task Manager, and then click the Processes tab.
4. Click Winword.exe, and then click End Process.
5. In the Task Manager Warning dialog box, click Yes. If you receive a message that states that the program is not responding,
click End Now.
6. Repeat steps d and e for each occurrence of Winword.exe.
7. On the File menu, click Exit Task Manager.
- Start Windows Explorer, and then browse to the folder that contains the document file that you tried to open when you received
the error message.
Delete the owner file.
The owner file is located in the same folder as the document that you tried to open. The owner file name uses the following
convention: It begins with a tilde (~), followed by a dollar sign ($),
followed by the remainder of the document file name. The file name
extension is .doc. For example, the owner file for Document.doc is
- Start Word. If Word asks you whether you want to load the changes that were made to the Global or Normal template, click No.
- Open your document.
Additional note for documents shared over a network:
If there are multiple people that could be editing the doc, it can sometimes be hard to figure out who might have the doc open. As shown on TechTalkMadness, the best way to find the answer is to use Computer Management on the system that hosts the shared file.
Computer Management -> System Tools -> Shared Folders -> Open Files to find out who has a document locked. If the user can't be contacted to disconnect themselves, you can forcefully do so by right clicking the locked file and selecting Close Open File (warning: the user might lose their changes).