I tried guessing what happens and it looks like a lot of changes were made to the code since I last fetched a copy of the swingx library.

I suggest that you get a more recent copy of it. It is somewhat difficult to get, but through some tricks, I got some valid links:
https://swingx.dev.java.net/files/do...swingx-1.0.zip
https://swingx.dev.java.net/files/do..._09_20-bin.zip

The first one corresponds to a milestone version of June 1st and the second one to a build from the state of the code on 20/09/2009.

In the first file, the swingx.jar is in the dist directory, in the second file, the file is in the root directory but has to be renamed to remove the date from the filename.

If things do not work, I suggest to work with the image of the current code and to report errors from there - that way my copy of the code is in line with the line numbers that will be reported for the errors.