When i started the launcher and hit "Play" and i sqw in development console i says "Failed Unpacking" This is the message i get from the development console :

[09:22:52 ERROR]: Couldn't unpack natives!
java.util.zip.ZipException: error in opening zip file
at java.util.zip.ZipFile.open(Native Method) ~[?:1.7.0_45]
at java.util.zip.ZipFile.<init>(Unknown Source) ~[?:1.7.0_45]
at java.util.zip.ZipFile.<init>(Unknown Source) ~[?:1.7.0_45]
at java.util.zip.ZipFile.<init>(Unknown Source) ~[?:1.7.0_45]
at net.minecraft.launcher.GameLauncher.unpackNatives(GameLauncher.java:466) ~[launcher.jar:?]
at net.minecraft.launcher.GameLauncher.launchGame(GameLauncher.java:212) [launcher.jar:?]
at net.minecraft.launcher.GameLauncher.onDownloadJobFinished(GameLauncher.java:616) [launcher.jar:?]
at net.minecraft.launcher.updater.download.DownloadJob.popAndDownload(DownloadJob.java:120) [launcher.jar:?]
at net.minecraft.launcher.updater.download.DownloadJob.access$000(DownloadJob.java:12) [launcher.jar:?]
at net.minecraft.launcher.updater.download.DownloadJob$1.run(DownloadJob.java:89) [launcher.jar:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.7.0_45]
at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.7.0_45]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [?:1.7.0_45]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [?:1.7.0_45]
at java.lang.Thread.run(Unknown Source) [?:1.7.0_45]