After installed Kubuntu, I already tried to use this but ran into an error. Today, as I had to enter my line up for the upcoming match of this evening, I decided to see if I could fix this problem. Indeed, the problem is fixed, and it seems to be pretty easy.
The problem was described on The HO forums, and the solution was also listed. Apparently, Kubuntu comes with an open source version of Java, not the Sun version. I had the choice of either installing the Sun version, or using the Sun version if it was already present on my system. It is already on my system, as I am a happy user of Zend Studio. So the problem was easily solved. I just edited my HO.sh, which launches Hattrick Organizer. Problem solved. I can again use Hattrick Organizer without a problem :) That's the power of a support community for you.