I was running on the nightly version and one day the presentation changed from my setting of Eclipse 2.1 style to the classic presentation. I went to change it back and I keep getting this error when I try I click on the General > Appearance option in preferences. After clicking OK, if I again click on the option, I get the results in the second screenshot. After much searching and finding no solution and no ticket created, I have switched to the beta release branch where the issue is not occurring. The third screenshot shows how the dialog appears in the beta release.