I have the IDEA CE sources checked out at C:\idea, and can build and run IDEA from within itself with no problems. However, all it takes is to add a new module, a plugin, and most if not all of the IDEA sources are shown in red. This happens whether the new module is outside C:\idea, in C:\idea or in C:\idea\plugins.
I have made no changes to the sources, and the problem disappears as soon as I delete my module.
What should I look for to see what's triggering this?
I'm using IDEA 9.0.2, on Windows XP, with Java 1.6.0_20.