To prevent multiple authors from trying to modify the same object at the same time, objects lock when they are open.
Object locking across modules
A local lock is placed on an object when you open it, and removed when you close the object. Other authors can open the object during this period, but can't edit the object. A blue local lock indicates that an object is open in the same module in which you're working. A local lock is indicated by in the object list.
When you open the library, a black lock appears when an object is open in the other module. For example, if you're working in Contribute and someone has opened an object in Author, you'll see the black lock in the object icon column against that object. An object opened in the other module is indicated by in the object list.
To see who has an object locked, open the object to display the locking information in the title bar.
Locks are released when an object is closed. In Contribute, a topic object should be closed by clicking the Close button at the right of the Editor pane.
If the computer that has an object locked doesn't close the object correctly - which can happen if you power off without exiting, your computer crashes, or other network problems occur - then the lock should clear after five minutes. If the lock doesn't clear after five minutes, contact your Author-it administrator about clearing the locks.