Diagnosis
The trace can only be activated for one user or group of users on eachapplication server.
Since the SQL trace is already activated for the specified user, youcannot activate the SQL trace, nor any of the other performance traces(RFC trace, HTTP trace, enqueue trace, buffer trace) on this applicationserver.

Procedure
Wait until the other user deactivates the trace. You can then activatethe SQL trace and other traces.
You can also activate the trace for all users, or for users whose namesmatch a pattern. In this case, specify the pattern in the usual format.
You can activate the trace for multiple users by choosing the button"Activate Trace with Filter".