So I was checking/loading a table schema for a table when I ran into this problem.
Something looked off in the default "Load" of table, so I went and tried to check "Use DBMS_METADATA (>=9i)". I got "ORA-01403: no data found" which then produced a message. After dismissing the message box and trying to do anything else produces another one "ORA-03127: no new operations allowed until the active operation ends".
I am running against 10.2.0.4 Oracle server.