What does "OSStatus error -36" mean in Time Machine?

Question

I'm getting intermittent errors with Time Machine. It will not back up to my external HD (LaCie d2 quadra). When this happens, the external HD cannot even by ejected (by Finder or Disk Utility). I have to turn it off. When I turn it back on and run Disk Utility Repair Disk it always says that the LaCie appears OK.
I don't know what's going on, but I'm suspecting it's the HD.
Any help?
The log says:
Dec 19 12:04:56 Roy-PowerBook com.apple.backupd[31851]: Starting standard backup
Dec 19 12:09:58 Roy-PowerBook com.apple.backupd[31851]: Error determining directory contents for /Volumes/LaCie 3TB: Error Domain=NSCocoaErrorDomain Code=256 UserInfo=0x100507400 "The file “LaCie 3TB” couldn’t be opened." Underlying Error=(Error Domain=NSOSStatusErrorDomain Code=-36 "The operation couldn’t be completed. (OSStatus error -36.)" (I/O error (bummers)))
Dec 19 13:12:33 Roy-PowerBook com.apple.backupd[31851]: error reading subpaths of directory /Volumes/LaCie 3TB/Backups.backupdb: Error Domain=NSCocoaErrorDomain Code=256 UserInfo=0x100510530 "The file “Backups.backupdb” couldn’t be opened." Underlying Error=(Error Domain=NSOSStatusErrorDomain Code=-36 "The operation couldn’t be completed. (OSStatus error -36.)" (I/O error (bummers)))

Answer 1

Thank you. I'd already been to Pondini's TM FAQs and had suspected that the problem was corrupted files or bad media. Only DriveGenius DrivePulse has ever given me any error messages about that LaCie, and it said only that the drive had errors and needed repair ASAP. Disk Utility of course found nothing to repair. A tech at ProSoft suggested corrupted files, saying bad TM files often cannot be detected by normal means and that then the only solution is as you said: backup, reformat, and restore the LaCie.
Unfortunately, the Backups.backupdb file is about 1.5 TB and I didn't have another drive that big to back up to. Now I do, so following the directions in "Time Machine: How to transfer backups from the current backup drive to a new backup drive" I backed up the backup to a new OWC drive. (The copying took about 20 hours.)
I certainly can't trust the LaCie until I can ascertain whether the errors were caused by corrupt files or bad media. At this point, I have little idea how to do that. After the holidays, I'll look into it.