This message can appear if another program is currently using the file that you are editing. For example, if a table or paragraph ...

This message can appear if another program is currently using the file that you are editing.  For example, if a table or paragraph in your document was linked to by another application and that application is currently open and running (possibly on another computer or an application running on your computer that you cannot see).  This can also happen whenever you are in a shared environment and file locking is enabled by another application.