As has been said many times, upgrading OS's is a dangerous operation
at the best of times and the changes that 11.04 makes are a lot more
demanding than most so it's not surprising that reports of updates
that have failed are prominent !

Unfortunately, once an update has screwed up the most permanent way to
fix it is to start all over again - there are ways to try and repair
through command line that can be tried but IMHO you can never be sure
that the repair is anything other than a fudge that will bite you hard
at some time in the future