I got the same error after installing WindowBuilderPro.
Using current Eclipse 3.3 Europa.
I did remove all files in config-dir, except config.ini, platform.xml and bookmarks.xml as stated in installation instructions.
After unzipping the files into the eclipse folder I also got the message "The Eclipse executable launcher was unable to locate its companion shared library."
I'm totally new to eclipse and java, so please give me an answer at beginners level
(I do not really understand what was discussed before in this thread...)
Thanks in advance