You receive the read banner error stating "This policy is currently being edited by another user. Please try again later" when you try to edit a policy.
No other users are editing the policy.
The best way to resolve the "Unable to edit policy - Policy is in use by another user" or "This policy is currently being edited by another user. Please try again later" issue is to restart the SymantecDLP services on the Enforce server.
There may be some sort of indication of what the problem is in the Tomcat log, but it is likely some sort of lock that can only be cleared by a restart of the services.
You can check in the latest localhost log to confirm that a user is still logged in and not logged out.
NOTE: As an alternative, you can wait for the timeout period to expire (approx. 30 minutes) if you do not want to restart the SymantecDLP services. Or you can also only try restarting the Manager service to see if that works.