Andrew, did you read the reference note Joel posted? There was a section that mentioned the need to run DBMS_AUDIT_MGMT.INIT_CLEANUP to get Oracle to switch from updating to just inserting. There is also another note I found that mentions the need to add an index on one of the timestamp columns for the dbms_audit_mgmt purge routines. The same note warns adding an index is officially unsupported however it suggest adding it if you need it which is likey if you have a large audit table. This is however a different index from the origional.