I noticed in the database that the table tbllog_register has over 89,000 records in it, and tblactivitylog has over 12,000. I have Settings -> General Settings -> Limit Activity Log set to 1000, which apparently doesn't appear to be working for tblactivitylog, although the documentation does say, "Non client related entries will remain." I took a look at Utilities -> System -> System Cleanup, and none of the tools there appear to apply to the table tbllog_register. On that page,