Errors when transferring Time Machine to a new drive
I am in the same situation: I am trying to move my Time Machine backup from a 1TB LaCie d2 Quadra disk to a new 3TB LaCie Quadra, both on FireWire 800. I have followed the same Apple instructions as you and get a bunch of -50 errors after a while.

My current approach is to repartition the new drive and use:

sudo cp -R /Volumes/OldTimeMachine/Backups.backupdb /Volumes/NewTimeMachine


but I don’t know if that will copy things correctly. My reading of the man page for cp suggests that it should (this is OS X 10.7.5).

I found this thread on MacRumors Forum which may explain things, although I am not sure. If using cp fails I will try updating the firmware in the older drive using the LaCie Firmware Updater for Mac from this support page and go back to using Finder to copy the backup.