failed update to 12.04
Not sure this is relevant, since this is an old post. Anyway, I had the same problem. And its not completely resolved yet. I did use the live boot option with a disk and did a reinstall, trying to save my old data. This worked to some extent, as I was able to access the section of the hard drive that had my old data. BUT, like you, I had access issues,as the system reported I was not the owner of some of the files. I used the terminal program with the CHOWN command to switch ownership of the files.
if you use sudo chown You -R Oldspot it should allow you to access the files.
In this example, You (equals your name in Linux), -R recursively fixes the whole dir, and Oldspot means the folder that you want to change ownership from. You should probably read the description of chown in the help file before you do this, but it really worked for me. I used Puppy (yet another version of Linux) to copy the files from one segment of my hard drive to another, then I used chown to enable the owner to change from whatever to me (Bob) in my case. The SUDO makes this a super user command so you can get the rights you need to solve this. I had great success with 12.04 on one computer and some complications on another. However, I still like it. Honestly, my main Linux box uses Linux Mint, and it is very stable so I like it very much. Hope you have solved your issues!