Can't compile plain Java project...

Hi,
using build #9815 and the latest release of the Scala plugin makes it impossible to compile a plain Java project.
Running "Build->Build project" opens a error message with the title "Cannot compile" and the message "Cannot compile Scala project. Please attach a scala-compiler.jar to any project module".

This is a Java 5 project with one module, no Scala files, no Scala facet set.

How can I workaround this problem?