Apple has warned that "critical file data" may be lost when using the sleep function and iBooks and FireWire PowerBooks.

On the company’s Technical Information Library, Apple said: "[There is] a potential data loss issue associated with using the "Preserve memory contents on sleep" option available in the Energy Saver control panel. This option is available on iBook and PowerBook (FireWire) computers."

Following such loss, when an iBook user starts up from the system CD the hard drive may not mount, and Disk First Aid may be unable to fix the problem. Sometimes the only option is to reinitialize the drive.

Apple is currently working on a fix for this problem, and until then recommends deselecting the "Preserve memory contents on sleep" option for both battery and power adaptor settings.