I am running WindowBuilder Pro 6.8 + Eclipse 3.4 on Java 1.5.0_16-b06-284, Mac OS X 10.5.5. For some of my Java Swing apps, when I switch to designer view and then again when I perform nearly any operation, I get a popup dialog from WIndowBuilder "Unable to find *.class file for compilation unit ... that exists in Java project. Do you have autobuild enabled?". Yes, I have autobuild enabled, and the problem seems related to the use of subclasses of JPanel within my code. These JPanel subclasses are just missing in the design view (hierarchy and layout panes), although they are fine at runtime. The "Unable to find *.class file..." always refers to the class I am viewing, not to the JPanel subclass, but it seems to be occuring only when there a subclassed JPanel elements in the design.
The exact same source files work fine in Win XP (same Eclipse + WindowBuilder version), where the subclassed JPanels are visible in the hierarchy and in the layout panes.
There are no unusual messages in the Eclipse .log.
This is a showstopper on Mac OS X since JPanel subclasses are basically being ignored. Attached are screen clips of the same file opened in Eclispe in Mac OS X and Win XP -- notice that the center content pane is dropped on the Mac.