Are you using wireless? Upgrade installed OS on the computer can lead to issues.
Also there is an update to the update for Lion. I think this is what you installed.
The problem is probably just TM is lousy.. use CCC or superduper until Apple decide to put some programmers back doing network or OSX work.
You can just erase the TC..
You can also verify the sparsebundle.
Large backups over wireless IMHO are more the issue than bad hard disk sectors.
An update should be relatively small.. a couple of hundred MB up to 1GB .. a 150GB update is I hope a full backup.