Today I upgraded a bunch of machines to the latest Kubuntu offering, version 9.04, or "Jaunty Jackalope". Well, it was all going a bit too well and when I came to upgrade my main work machine, a thinkpad T400, I ran into problems. There are a couple more kinks but I had one particular error which I wanted to blog about. When I upgraded and then restarted Kubuntu, it froze on the splash screen after showing three icons (up to the globe).
The problem was that the files in the ~/.ICEauthority directory were owned by root so couldn't be written to by my user. I followed the instructions I found on this post where someone had exactly the same problem, and just chowning the whole directory to my user fixed the problem and allowed me to boot Kubuntu.
Hopefully if anyone else has this problem they'll find either this post or the other one and also find the easy fix! If this works for you, leave a comment.