In the nightlies it is possible to get the below exception. The reason for this is that the compiled classes only depend on the Scala version and not on the compiler version, which means that if a nightly is updated, it is very likely that the code breaks due to binary incompatibilities.

2015-11-16 10:24:27,554 ERROR [ForkJoinPool-1-worker-5] - org.scala-ide.sdt.core - org.scala-ide.sdt.core - org.scala-ide.sdt.core - 2 - Problems occurred when invoking code from plug-in: "org.scala-ide.sdt.core".
java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at org.scalaide.core.internal.extensions.ExtensionCompiler$$anonfun$13$$anonfun$apply$4.apply(ExtensionCompiler.scala:281)
	at org.scalaide.core.internal.extensions.ExtensionCompiler$$anonfun$13$$anonfun$apply$4.apply(ExtensionCompiler.scala:280)
	at org.scalaide.ui.internal.editor.SaveActionExtensions$$anonfun$org$scalaide$ui$internal$editor$SaveActionExtensions$$createExtensionWithCompilerSupport$1.apply(SaveActionExtensions.scala:273)
	at org.scalaide.ui.internal.editor.SaveActionExtensions$$anonfun$org$scalaide$ui$internal$editor$SaveActionExtensions$$createExtensionWithCompilerSupport$1.apply(SaveActionExtensions.scala:266)
	at org.scalaide.core.compiler.InteractiveCompilationUnit$$anonfun$withSourceFile$1.apply(InteractiveCompilationUnit.scala:202)
	at org.scalaide.core.compiler.InteractiveCompilationUnit$$anonfun$withSourceFile$1.apply(InteractiveCompilationUnit.scala:202)
	at org.scalaide.core.internal.compiler.PresentationCompilerProxy$$anonfun$internal$1.apply(PresentationCompilerProxy.scala:105)
	at org.scalaide.core.internal.compiler.PresentationCompilerProxy$$anonfun$internal$1.apply(PresentationCompilerProxy.scala:104)
	at scala.Option.flatMap(Option.scala:171)
	at org.scalaide.core.internal.compiler.PresentationCompilerProxy.internal(PresentationCompilerProxy.scala:104)
	at org.scalaide.core.internal.compiler.PresentationCompilerProxy.apply(PresentationCompilerProxy.scala:62)
	at org.scalaide.core.compiler.InteractiveCompilationUnit$class.withSourceFile(InteractiveCompilationUnit.scala:202)
	at org.scalaide.core.internal.jdt.model.ScalaSourceFile.withSourceFile(ScalaSourceFile.scala:73)
	at org.scalaide.ui.internal.editor.SaveActionExtensions$class.org$scalaide$ui$internal$editor$SaveActionExtensions$$createExtensionWithCompilerSupport(SaveActionExtensions.scala:266)
	at org.scalaide.ui.internal.editor.SaveActionExtensions$$anonfun$3$$anonfun$apply$5.apply(SaveActionExtensions.scala:166)
	at org.scalaide.ui.internal.editor.SaveActionExtensions$$anonfun$3$$anonfun$apply$5.apply(SaveActionExtensions.scala:166)
	at org.scalaide.util.eclipse.EclipseUtils$$anon$3.run(EclipseUtils.scala:216)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
	at org.scalaide.util.eclipse.EclipseUtils$.withSafeRunner(EclipseUtils.scala:212)
	at org.scalaide.ui.internal.editor.SaveActionExtensions$$anonfun$3.apply(SaveActionExtensions.scala:165)
	at org.scalaide.ui.internal.editor.SaveActionExtensions$$anonfun$3.apply(SaveActionExtensions.scala:171)
	at org.scalaide.util.internal.FutureUtils$TimeoutFuture$$anonfun$1.apply(FutureUtils.scala:27)
	at org.scalaide.util.internal.FutureUtils$TimeoutFuture$$anonfun$1.apply(FutureUtils.scala:27)
	at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)
	at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
	at scala.concurrent.impl.ExecutionContextImpl$AdaptedForkJoinTask.exec(ExecutionContextImpl.scala:121)
	at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
	at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
	at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
	at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
Caused by: java.lang.AbstractMethodError: org.scalaide.core.internal.generated.AddMissingOverrideCreator$$anon$1.scala$tools$refactoring$transformation$TreeTransformations$_setter_$findBestPackageForImports_$eq(Lscala/tools/refactoring/transformation/Transformations$Transformation;)V
	at scala.tools.refactoring.transformation.TreeTransformations$class.$init$(TreeTransformations.scala:144)
	at org.scalaide.core.internal.generated.AddMissingOverrideCreator$$anon$1.<init>(<memory>:12)
	at org.scalaide.core.internal.generated.AddMissingOverrideCreator.create(<memory>:12)
	... 34 more