Diagnosis
The trace can only be activated for one user or group of users on eachapplication server.
Since a trace has already been activated for the specified user in ST01,you cannot activate any of the performance traces (SQL trace, RFC trace,HTTP trace, enqueue trace, buffer trace) on this application server.

Procedure
Wait until the other user deactivates the trace. You can then activatethe performance 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".