The second fix requires starting up in single-user mode by holding Command-S after restarting the computer, then executing a series of commands that will remove the offending software. However, according to Apple. if the problem still exists after uninstalling APE, you may need to resort to the first, recommended fix: performing an Archive and Install. ----- A number of users who have bought Mac OS X Leopard have been experiencing stalled upgrade installations, Apple's forums reveal. Upon nominally completing the installation process, some Macs have rebooted only to become stuck at a blue screen, requiring users to manually shut them down. Apple is said to already be aware of the issue, but the exact causes are at present unknown; some have suggested problems with attached peripherals, DivX Application Support or Tiger's RAID technology, but these factors are not constant. A recurring suggestion is the presence of Unsanity's Application Enhancer program, though this too has not been reported on all frozen Macs. MacFixit has posted a guide for removing Application Enhancer, as well as handling other potential fixes. The site ultimately recommends though that if installations continue to freeze, users should attempt to boot from the Leopard DVD by holding down "C" at start-up, and picking either "Archive and Install" or "Erase and Install" instead of the Upgrade option. Apple on Saturday released a patch for less severe issues, fixing Wi-Fi connections, logins for users upgrading from Mac OS X 10.1, and password changes for FileVault-protected accounts.