Persistence has once again paid off. I solved the 5.1.4 update issue by realizing that I could deceive the installer by deleting the /library/receipts/IEUpdater file. It would have no previous version update history to read from, effectively eliminating any chance of an error. It seemed likely that the previous version history, not the system update history, was causing the problem. After all, IE is a third-party app. Why would a System software update prevent an unrelated app from updating? Even with Apple's silly order-of-update madness, it just didn't make any sense. Thanks for all replies......