A significant number of Mac owners upgrading to Leopard reported that after installing the new operating system, their machines locked up, showing only an interminable -- and very Windows-like -- "blue screen of death."

Easily the heaviest-trafficked thread on the Leopard support forums, "Installation appears stuck on a plain blue screen" told how after a successful Leopard install using the default "Upgrade" option and the required restart, some users' Macs refused to budge from the blue screen. Although many gave up after 30-60 minutes and rebooted, others were more patient and let their Macs be as long as six hours.

"Hmmmm. I feel like a windoze user now," said Doug Mcilvain. I have re-installed and it has been sitting there with a blue screen for 4 1/2 hours."

Almost everyone who added to the thread -- which included more than 200 messages and over 7,400 views by 10:30 p.m. Friday, Pacific time -- selected the Upgrade option. Set as the default, Upgrade is the least intrusive of the three install options. "Most of your existing settings and applications are left untouched during an upgrade," Apple states in an online support document. In fact, some reports speculated that the glitch might be related to a third-party program that installs a base-level framework that modified OS X.

Frustrated users who rebooted to the install DVD then upgraded a second time using the "Archive and Install" option reported success, and no lingering blue screen after restart. "I grew impatient after the first hour and rebooted to DVD and then reinstalled choosing the Archive/Install option," said volksapple. "That worked just fine. Despite this small hiccup, it's far better than any Windows upgrade I've suffered through."

Other users, however, waited it out, or were told to by Apple support personnel. One user, James Mitchell9, said the blue screen finally vanished at the 75-min. mark. Others claimed they had been told the long blue-screen-of-pause could last as long as two, or even three, hours.

Still others jumped in with instructions to manually uninstall APE (Application Enhancer), a framework created by Unsanity for use with its Mac customizing haxies such as ShapeShifter. "Please note that this does involve manipulation of files from the root prompt," cautioned Chris Mcculloh, who first made the suggestion. "This is not for the faint of heart, or those who are unfamiliar with the UNIX file system/command structure."

Mcculloh listed the steps as:

• * Reboot into single-user mode (hold Command-S while booting)
• * Remove the following files by typing each line below:
• rm -rf /Library/Preference Panes/Application Enhancer.prefpane
• rm -rf /Library/Frameworks/Application Enhancer.framework
• rm -rf /System/Library/SystemConfiguration/Application Enhancer.bundle
• rm -rf /Library/Preferences/com.unsanity.ape.plist
• * Exit, to continue booting normally, type:
• exit

For those who have not yet installed Leopard, the Unsanity APE app provides an uninstaller that can be used first to remove the framework before the new OS is installed. Alternatively, users can use the "archive and install" option, which places a new copy of Leopard on the user's computer while moving older OS files to another folder. That would have the effect of moving the potentially offending APE software to a location where it can do little to interfere with the installation process.

Apple was not available for comment Friday night, but an Australian user claimed support said the phones had been ringing "non-stop" over the problem since 9 a.m. local time. Australia was one of the first countries where Mac users got their hands on Leopard.

A few took the install screw-up in stride, or at least kept their sense of humor. "I don't remember seeing the option in setup under Installation Type that said 'Wait indefinitely while you stare at a blue screen and eventually go mad'," said Phill Horrocks1.

Computerworld's Ken Mingis contributed to this report.