Crash

getting an error ant can't start MC

java.lang.NullPointerException
	at net.minecraft.launcher.GameLauncher.cleanOldNatives(GameLauncher.java:514)
	at net.minecraft.launcher.GameLauncher.launchGame(GameLauncher.java:359)
	at net.minecraft.launcher.GameLauncher.onDownloadJobFinished(GameLauncher.java:690)
	at net.minecraft.launcher.updater.download.DownloadJob.popAndDownload(DownloadJob.java:124)
	at net.minecraft.launcher.updater.download.DownloadJob.access$000(DownloadJob.java:15)
	at net.minecraft.launcher.updater.download.DownloadJob$1.run(DownloadJob.java:94)
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)