[Haskell-beginners] Could not find file in module graph

Hi! I'm using version 2.0.4 of Eclipse FP and I very often get an error saying "Could not find file in module graph.". I did a quick search on the web for this message, but all I could find was some old threads discussing an issue with this symptom (for instance http://code.google.com/p/scion-lib/issues/detail?id=36#c1). Does anyone know what the error means and how I can avoid it? -- Mvh Øystein Kolsrud