ScalaIDE and cryptic ClassNotFound errors - scala

Question

The problem
Using Scala IDE, I've been getting a cryptic NullPointerException wherein the classed underneath "src/test/scala" are not found... My IDE Details are :
Related
A related question (see http://www.stackoverflow.com/questions/9686517/scala-eclipse-plugin-java-lang-classnotfoundexception) was answered some time (2 years ago), but it appears I'm seeing the same error in new ScalaIDE (downloaded for 2.10, just a week ago).
System Details and stacktrace
eclipse.buildId=3.0.3-20140327-1716-Typesafe
java.version=1.7.0_55
java.vendor=Oracle Corporation
BootLoader constants: OS=macosx, ARCH=x86_64, WS=cocoa, NL=en_US
Framework arguments: -keyring /Users/bigpetstore/.eclipse_keyring -showlocation
Command-line arguments: -os macosx -ws cocoa -arch x86_64 -keyring /Users/bigpetstore /.eclipse_keyring -showlocation
And the exception is as follows
java.lang.NullPointerException
at scala.collection.convert.Wrappers$JEnumerationWrapper.hasNext(Wrappers.scala:46)
at scala.collection.Iterator$$anon$11.hasNext(Iterator.scala:327)
at scala.collection.Iterator$class.toStream(Iterator.scala:1143)
at scala.collection.AbstractIterator.toStream(Iterator.scala:1157)
at scala.collection.TraversableOnce$class.toIterable(TraversableOnce.scala:259)
at scala.collection.AbstractIterator.toIterable(Iterator.scala:1157)
at scala.tools.eclipse.ScalaPlugin.sbtCompilerInterface$lzycompute(ScalaPlugin.scala:177)
at scala.tools.eclipse.ScalaPlugin.sbtCompilerInterface(ScalaPlugin.scala:177)
at scala.tools.eclipse.buildmanager.sbtintegration.SbtInputs$$anon$5.scalac(SbtInputs.scala:71)
at scala.tools.eclipse.buildmanager.sbtintegration.SbtInputs$$anon$5.scalac(SbtInputs.scala:63)
at sbt.compiler.IC$.compile(IncrementalCompiler.scala:21)
at scala.tools.eclipse.buildmanager.sbtintegration.EclipseSbtBuildManager.runCompiler(EclipseSbtBuildManager.scala:133)
at scala.tools.eclipse.buildmanager.sbtintegration.EclipseSbtBuildManager.update(EclipseSbtBuildManager.scala:124)
at scala.tools.eclipse.buildmanager.sbtintegration.EclipseSbtBuildManager.build(EclipseSbtBuildManager.scala:178)
at scala.tools.eclipse.ScalaProject.build(ScalaProject.scala:666)
at scala.tools.eclipse.ScalaBuilder.build(ScalaBuilder.scala:119)
at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:733)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:206)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:246)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:299)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:302)
at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:358)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:381)
at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:143)
at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:241)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)

Answer 1

Oddly, I was actually able to fix this, by simply switching from SBT to the refined compiler:
Any thoughts on why the SBT compiler would work but "refined" would fail, I'd like to hear.
There are some related threads, but no definitive answer (yet) that i can see about why it is that SBT would throw an NPE when compiling. Could just be an accidental error or bug in the plugin itslef that I was triggering.
https://groups.google.com/forum/#!msg/scala-ide-user/Tscp9sLixJI/a52OR068dYAJ
https://groups.google.com/forum/#!msg/scala-ide-user/H3ov9hBt5aA/uctURBzV2JwJ