Diagnosis
You tried to edit a system object (especially a program source text ordata element) but you are already editing that object in anothersession. You cannot change the object twice in this way.

System Response
The system does not allow you to edit the object.

Procedure
Edit the object in your other session, or release the object in theother session.
Special case: If your SAPGUI session has crashed but your session withthe R/3 server is not terminated, you can proceed as follows:
RESET N1
Try to transfer the session (Transaction SM04, find your old usersession and restart it using Edit -> Transfer session .
If this is not successful, exit the old session with Edit -> Deleteuser.
Caution: Ensure that you exit the correct session on the correct R/3server.