"No root file system is defined"

"No root file system is defined" This error I got when I tried to reinstall Xubuntu after a first install that went ok but was corrupted. The reason of this corruption was that I tried to make a triple boot configuration (Puppy Linux, Xubuntu and Win2000- more about that later). But this proved of no importance to solve this problem:

The solution to this problem was very simple.
My mistake was that I had already partitioned the hard drive for Linux with Partition Magic, so from Win 2000.
What I should have done and did later was resize my Windows partition first and create unused space (with Partition Magic) and than let gparted, the linux partitioner do the rest of the job of partitioning during the (X)ubuntu install. The most simple and effective way was of course to let the Ubuntu install do the whole job. But that you get when you have to leave trusted tools; you keep using them as long as possible...