According to posts appearing in the discussion forum on Apple's support Web site, Macs upgraded to version 10.4.11 of Tiger are freezing up and refusing to reboot without a clean installation.
As a result, users say they're losing music and video files they've paid for and important data is being lost.
Apple does "not see any issues at all with having an update that can cause this type of catastrophic failure," poster 'ggalat', a Mac user from Georgia, wrote on the forum.
The Georgia resident's MacBook Pro crashed after the update and has remained that way ever since, according to the post. Technicians at the local Apple Store's 'Genius Bar' said the machine's hard drive would have to be wiped clean in order to be restarted, according to the post.
Mac user 'hum dizzle' reported that "I have had the same issue," as did a poster going by the name 'briken.' Several others on the forum also said they experience unrecoverable crashes after upgrading to Tiger 10.4.11.
The culprit, according to some posters on the forum and published reports, may be Boot Camp -- a utility that allows Mac users to run Microsoft Windows on their computers. Some users recommend eliminating the utility before upgrading to the latest version of Tiger.
For its part, Apple warns users that upgrading to 10.4.11 may cause issues with "third party" software -- but the company is mum on problems related to its own Boot Camp product.
Mac OS 10.4.11 is designed to offer Tigers users a number of improvements, including better synching between Yahoo and iPhone address books, more compatibility with third party WAN devices, and improved font support for Quark Xpress pagination software.
It's likely, however, that many users will shy away from the upgrade until Apple posts an official fix for the system-crashing bug.
The user reports echo some of the complaints voiced by Apple customers who've upgraded their systems to Leopard, which Apple introduced in October. Many Leopard users recently said their computers displayed the so-called "blue screen of death" after they upgraded from Tiger.
The timing of such reports couldn't be worse for Apple. The company has spent millions to launch a high profile TV advertising campaign -- Mac vs. PC--designed to promote its products as a more reliable, user-friendly alternative to systems based on Microsoft Windows.