Apple has addressed some of the problems Leopard users have reported with Time Machine, including stalled and invisible backups, with several support documents.

Mac users, however, are still packing Apple's support forums with complaints about the backup and restore software.

Initial Time Machine backups have been problematic since Leopard launched Oct. 26, with scores of users reporting that the software would stall after as little as 10GB or as much as 90% of the entire data set had been copied to the external drive. Most said they had received the error message: "Unable to complete backup. An error occurred while copying files to the backup volume."

According to Apple, the fault is in the external drive's partitioning.

"Some hard disks ship with a Master Boot Record (MBR) partition type," Apple said in a support document posted at the start of this week. "You will need to erase the external disk so that it is supported by Time Machine."

Macs running on PowerPC processors should reformat the drive with Disk Utility, and repartition it using the Apple Partition Map scheme; Intel-based Macs, on the other hand, should select the GUID partition scheme. "Once the external hard disk is reformatted, select it again in Time Machine preferences and use it for your backups," Apple added.

Another Apple document spelled out a bug that prevents users from seeing backups, even though Time Machine has successfully copied data. The culprit: non-alphanumeric characters in the computer's name.

"Past backups may not appear if your computer name includes certain characters," said the note, dated Monday. The only acceptable characters are the English alphabet, lower- and uppercase, and the numbers 0-9. The computer's name is set in the Sharing Preferences panel.

Users posting to the Time Machine support discussion, however, claimed that the backup software's problems went beyond the two problems Apple addressed. According to the forum's threads, problems include Time Machine corrupting drives, the program faltering before it finishes restoring a backup and the deletion of files from backups before the external drive has been filled.

Some were clearly at their wit's end.

"Time Machine does NOT work," said a user identified as Applemans. "Changing hard disk names: with or without spaces, characters etc., erasing hard disks, reinstall Leopard. It simply doesn't matter what you do, how you do it."

Theories abounded on the forum as to causes for the various Time Machine snafus. Many users took LaCie Ltd. to task because they were using hard drives from that maker, a popular supplier of external disks to the Mac market. Someone purportedly from LaCie waded in on one thread: "LaCie has shipped a few million drives to Mac users over the years," said someone tagged as LaCie FireWire. "Many more than other vendors. It makes sense then that there will be a high proportion of LaCie drives in use by Mac users."