This message is typically due to a temporary disconnection between the database and the TapRooT® software. As a safety measure, the document you had open at the time stays locked to keep other users from accidentally overwriting your work. Now it's just waiting to be told that it's OK to let that document be edited again.  

To clear the locked SnapCharT, click on the Admin tab at the top and scroll to the bottom of that page. In the bottom left corner, there is a lock icon. Click the lock to release the locked SnapCharT. You can now go back and edit the chart.

You must have access to the Admin menu to clear the locks.