Sooo, what is happening here?

[error] error while loading Diff, class file needed by Diff is missing.
[error] reference type Serializable of package scala refers to nonexisting symbol.
[error] class file needed by Diff is missing.
[error] reference type Serializable of package scala refers to nonexisting symbol.
[error] two errors found
[debug] Compilation failed (CompilerInterface)
Compilation failed
	at xsbt.CompilerInterface.run(CompilerInterface.scala:93)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:57)
	at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:29)
	at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:25)
	at sbt.AggressiveCompile$$anonfun$6.compileScala$1(AggressiveCompile.scala:67)
	at sbt.AggressiveCompile$$anonfun$6.apply(AggressiveCompile.scala:79)
	at sbt.AggressiveCompile$$anonfun$6.apply(AggressiveCompile.scala:57)
	at sbt.inc.IncrementalCompile$$anonfun$doCompile$1.apply(Compile.scala:21)
	at sbt.inc.IncrementalCompile$$anonfun$doCompile$1.apply(Compile.scala:19)
	at sbt.inc.Incremental$.cycle(Incremental.scala:33)
	at sbt.inc.Incremental$.compile(Incremental.scala:20)
	at sbt.inc.IncrementalCompile$.apply(Compile.scala:17)
	at sbt.AggressiveCompile.compile2(AggressiveCompile.scala:87)
	at sbt.AggressiveCompile.compile1(AggressiveCompile.scala:38)
	at sbt.AggressiveCompile.apply(AggressiveCompile.scala:28)
	at sbt.Compiler$.apply(Compiler.scala:107)
	at sbt.Defaults$$anonfun$compileTask$1.apply(Defaults.scala:420)
	at sbt.Defaults$$anonfun$compileTask$1.apply(Defaults.scala:420)
	at sbt.Scoped$$anonfun$hf2$1.apply(Structure.scala:506)
	at sbt.Scoped$$anonfun$hf2$1.apply(Structure.scala:506)
	at scala.Function1$$anonfun$compose$1.apply(Function1.scala:44)
	at sbt.Scoped$Reduced$$anonfun$combine$1$$anonfun$apply$9.apply(Structure.scala:304)
	at sbt.Scoped$Reduced$$anonfun$combine$1$$anonfun$apply$9.apply(Structure.scala:304)
	at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:40)
	at sbt.std.Transform$$anon$5.work(System.scala:67)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:221)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:221)
	at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:13)
	at sbt.Execute.work(Execute.scala:227)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:221)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:221)
	at sbt.CompletionService$$anon$1$$anon$2.call(CompletionService.scala:26)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
	at java.util.concurrent.FutureTask.run(FutureTask.java:138)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
	at java.util.concurrent.FutureTask.run(FutureTask.java:138)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	at java.lang.Thread.run(Thread.java:680)
[error] {file:/Users/Mads/dev/projects/lifty_engine/}lifty-engine/compile: Compilation failed