Whatever I do when writing a plugin, I end up with all the IDEA sources in red. Any suggestions?

Hi,

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.

Thanks,
Ricky.