now i have more information:

2010-03-13 22:06:47,833 [  16139]   INFO - ij.compiler.impl.CompileDriver - COMPILATION STARTED
2010-03-13 22:06:47,984 [  16290]   INFO - lij.compiler.impl.CompilerUtil - Initial VFS refresh took 94 ms: 0 min 0sec
2010-03-13 22:06:48,258 [  16564]  DEBUG - la.compiler.ScalacOutputParser - scalac error: Parameter '-reset' is not recognised by Scalac.
2010-03-13 22:06:48,258 [  16564]  DEBUG - la.compiler.ScalacOutputParser - scalac error: Parameter '-reset' is not recognised by Scalac.
2010-03-13 22:06:48,258 [  16564]  DEBUG - la.compiler.ScalacOutputParser -   scalac -help  gives more information
2010-03-13 22:06:48,258 [  16564]  DEBUG - la.compiler.ScalacOutputParser -   scalac -help  gives more information
2010-03-13 22:06:48,258 [  16564]  DEBUG - la.compiler.ScalacOutputParser - scalac error: bad option: '-reset'
2010-03-13 22:06:48,258 [  16564]  DEBUG - la.compiler.ScalacOutputParser - scalac error: bad option: '-reset'
2010-03-13 22:06:48,258 [  16564]  DEBUG - la.compiler.ScalacOutputParser -   scalac -help  gives more information
2010-03-13 22:06:48,258 [  16564]  DEBUG - la.compiler.ScalacOutputParser -   scalac -help  gives more information
2010-03-13 22:06:48,586 [  16892]  DEBUG - la.compiler.ScalacOutputParser - 
2010-03-13 22:06:48,586 [  16892]  DEBUG - la.compiler.ScalacOutputParser - 
2010-03-13 22:06:48,586 [  16892]  DEBUG - la.compiler.ScalacOutputParser - 
2010-03-13 22:06:48,586 [  16892]  DEBUG - la.compiler.ScalacOutputParser - 
2010-03-13 22:06:48,663 [  16969]   INFO - lij.compiler.impl.CompilerUtil -     COMPILATION FINISHED; Errors: 1; warnings: 0 took 830 ms: 0 min 0sec

took me a while to find the secret logging option

weird thing is, i could not reproduce this error...it just appeared at a random point in time and wouldn't go away until i figured out i had to switch "reset fsc" off. it didn't matter if "use fsc" was checked or not. unchecking everything fixed the problem.

- IDEA version

- Scala plug-in version

- Scala version

-  Java version

- Operating system

- Processor architecture

if i had a more specific error message, i would have given some information - but "internal error" just gave me no hint what information could help.

i tried different builds of idea, the scala plugin, scala and different java versions, but the error persisted

it seems the project is broken. if i delete all scala files except a hello world -> still crashes

new project -> new module -> hello world -> works

new module in old project -> crash

i enabled the secret scala compiler logging option in some xml file and got the error message that "reset" is an unknown option. i looked at my compiler settings -> there is was, the evil checkbox. unchecked it, problem fixed.