"existing Logminer session"
*Cause: An attempt was made to execute DBMS_LOGMNR_D.SET_TABLESPACE while
a Logminer session(s) was active.
*Action: First cause all Logminer sessions to be closed. A Logminer
session can exist as a result of executing DBMS_LOGMNR.START_LOGMNR
or as the result of using Oracle features such as
Data Guard SQL Apply or Streams which use Logminer.
Next, execute DBMS_LOGMNR_D.SET_TABLESPACE.