I was having the same problems with TM backups failing in 10.6 (and 10.6.1). I tried all of the suggestions in this thread—throwing away preferences, reformatting hard drive, disk repair etc.—and nothing was working. I finally got mine to work. It turned out that TM was getting hung up on certain files inside packages, either installers or applications. I was able to trace them down by having console running at the same time and when the backup failed it would point me to the culprit. For instance... 9/10/09 3:43:56 PM com.apple.backupd Error: (-41) SrcErr:NO Copying /Applications/Transmit.app/Contents/Frameworks/FTPKit.framework/Versions/A/Head ers to /Volumes/Backup HD/Backups.backupdb/jscott/2009-09-08-093350.inProgress/42948351-27F0-4EB3-8605 -276275EB9746/Macintosh HD/Applications/Transmit.app/Contents/Frameworks/FTPKit.framework/Versions/A
This error pointed to my Transmit application. I deleted Transmit and ran a TM backup and it got a bit further until it hit another snag file. Rinse and repeat until the backup finally completed. In all there were 4 files TM couldn't get through. Deleting the package or updating the Application allowed TM to complete the backup. Good luck everyone!