The following exception occurs occasionally. Cleaning the cache directory resolves the issue, but happens again further down the track....

BuildingFAILURE:
> Building Build aborted because of an internal error.
> Building
> Building
> Building* What went wrong:
> BuildingBuild aborted because of an unexpected internal error. Please file an issue at: http://www.gradle.org.
> Building
> Building* Try:
> BuildingRun with
> Building --debug
> Building option to get additional debug info.
> Building
> Building* Exception is:
> Buildingjava.lang.ClassCastException: org.gradle.api.internal.changedetection.DefaultFileSnapshotter$FileCollectionSnapshotImpl cannot be cast to org.gradle.api.internal.changedetection.OutputFilesSnapshotter$OutputFilesSnapshot
> Building at org.gradle.api.internal.changedetection.OutputFilesSnapshotter$OutputFilesSnapshot.changesSince(OutputFilesSnapshotter.java:96)
> Building at org.gradle.api.internal.changedetection.OutputFilesChangedUpToDateRule$1.checkUpToDate(OutputFilesChangedUpToDateRule.java:43)
> Building at org.gradle.api.internal.changedetection.CompositeUpToDateRule$1.checkUpToDate(CompositeUpToDateRule.java:41)
> Building at org.gradle.api.internal.changedetection.DefaultTaskArtifactStateRepository$HistoricExecution.isUpToDate(DefaultTaskArtifactStateRepository.java:122)
> Building at org.gradle.api.internal.changedetection.DefaultTaskArtifactStateRepository$TaskArtifactStateImpl.isUpToDate(DefaultTaskArtifactStateRepository.java:154)
> Building at org.gradle.api.internal.changedetection.ShortCircuitTaskArtifactStateRepository$1.isUpToDate(ShortCircuitTaskArtifactStateRepository.java:35)
> Building at org.gradle.api.internal.changedetection.FileCacheBroadcastTaskArtifactStateRepository$1.isUpToDate(FileCacheBroadcastTaskArtifactStateRepository.java:37)
> Building at org.gradle.api.internal.tasks.execution.SkipUpToDateTaskExecuter.execute(SkipUpToDateTaskExecuter.java:44)
> Building at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:57)
> Building at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:41)
> Building at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:51)
> Building at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:52)
> Building at org.gradle.api.internal.tasks.execution.ExecuteAtMostOnceTaskExecuter.execute(ExecuteAtMostOnceTaskExecuter.java:42)
> Building at org.gradle.api.internal.AbstractTask.execute(AbstractTask.java:237)
> Building at org.gradle.execution.DefaultTaskGraphExecuter.executeTask(DefaultTaskGraphExecuter.java:167)
> Building at org.gradle.execution.DefaultTaskGraphExecuter.doExecute(DefaultTaskGraphExecuter.java:160)
> Building at org.gradle.execution.DefaultTaskGraphExecuter.execute(DefaultTaskGraphExecuter.java:78)
> Building at org.gradle.execution.TaskNameResolvingBuildExecuter.execute(TaskNameResolvingBuildExecuter.java:113)
> Building at org.gradle.execution.DelegatingBuildExecuter.execute(DelegatingBuildExecuter.java:54)
> Building at org.gradle.initialization.DefaultGradleLauncher.doBuildStages(DefaultGradleLauncher.java:158)
> Building at org.gradle.initialization.DefaultGradleLauncher.doBuild(DefaultGradleLauncher.java:112)
> Building at org.gradle.initialization.DefaultGradleLauncher.run(DefaultGradleLauncher.java:80)
> Building at org.gradle.launcher.RunBuildAction.execute(RunBuildAction.java:41)
> Building at org.gradle.launcher.RunBuildAction.execute(RunBuildAction.java:27)
> Building at org.gradle.launcher.ExceptionReportingAction.execute(ExceptionReportingAction.java:32)
> Building at org.gradle.launcher.ExceptionReportingAction.execute(ExceptionReportingAction.java:21)
> Building at org.gradle.launcher.CommandLineActionFactory$WithLoggingAction.execute(CommandLineActionFactory.java:219)
> Building at org.gradle.launcher.CommandLineActionFactory$WithLoggingAction.execute(CommandLineActionFactory.java:203)
> Building at org.gradle.launcher.Main.execute(Main.java:55)
> Building at org.gradle.launcher.Main.main(Main.java:40)
> Building at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> Building at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
> Building at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> Building at java.lang.reflect.Method.invoke(Method.java:597)
> Building at org.gradle.launcher.ProcessBootstrap.runNoExit(ProcessBootstrap.java:46)
> Building at org.gradle.launcher.ProcessBootstrap.run(ProcessBootstrap.java:28)
> Building at org.gradle.launcher.GradleMain.main(GradleMain.java:24)
> Building
> Building
> BuildingBUILD FAILED