dbms_xplan in SQL*Plus and serveroutput is enabled, an error message as shown below will be thrown: NOTE: cannot fetch plan for SQL_ID: 9babjv8yq8ru3, CHILD_NUMBER: 1
Please verify value of SQL_ID and CHILD_NUMBER;
It could also be that the plan is no longer in cursor cache (check v$sql_plan)
v$sql_plan is misleading in that case. The error message can be turned of with a SQL> set serveroutput off