dbms_system package

I just want t o generate a trace file for some session .

But i am getting following error when i execute below sql.

SQL> execute dbms_system.set_sql_trace_in_session(15,4300,true);
BEGIN dbms_system.set_sql_trace_in_session(15,4300,true); END;

*
ERROR at line 1:
ORA-06550: line 1, column 7:
PLS-00201: identifier 'DBMS_SYSTEM.SET_SQL_TRACE_IN_SESSION' must be declared
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored


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when i see this package using TOAD , i could see
package dbms_system wrapped message. What could be the reason for this ? what is the solution ?

thanks in advace

try

execute sys.dbms_system.set_sql_trace_in_session(15,4300,true);

Regards
Gert

thanks