time machine is not working on imac intel i7

I just got a new imac intel core i7 which is an upgrade from my power mac G4 MDD which I got in 2003. I transferred all the information from the power G4 using time machine and it worked fine. I then upgraded the OS to 10.6.4 given imac is intel core. All programs are working fine except I am unable to use time machine. It runs for a few gb and then the following error come on time machine buddy:

Starting standard backup
Backing up to: /Volumes/Backups/Backups.backupdb
Ownership is disabled on the backup destination volume. Enabling.
Backup content size: 237.9 GB excluded items size: 818.0 MB for volume Macintosh HD
No pre-backup thinning needed: 284.58 GB requested (including padding), 930.57 GB available
Waiting for index to be ready (101)
Indexing a file failed. Returned 1 for: /System/Library/Frameworks/Python.framework/Versions/2.5/Extras/lib/python/wx-2 .8-mac-unicode/wx/lib/floatcanvas/Utilities/ _init_.py, /Volumes/Backups/Backups.backupdb/van (5)/2010-08-17-184416.inProgress/75B311E0-7C50-4BD3-B7AD-03E3A1B883B2/Macintosh HD/System/Library/Frameworks/Python.framework/Versions/2.5/Extras/lib/python/wx -2.8-mac-unicode/wx/lib/floatcanvas/Utilities/ _init_.py
Aborting backup because indexing of file failed.
Stopping backup.
Copied 70375 files (17.4 GB) from volume Macintosh HD.
Copy stage failed with error:11
Backup failed with error: 11

Then when I try to verify and repair the disk, it does do it and keep on showing: " invalid node structure, invalid key length and invalid record count"

I have changed the external hard drive twice so I doubt that is the problem. Please help