Fatal error launching game. Report this to http://mojang.atlassian.net please!

my minecraft launcher told me Fatal error launching game. Report this to http://mojang.atlassian.net please! So here i am, i'm not sure whats wrong so i'm going to copy what came after the please report this, i'm not very good with computers so this is the best i could do sorry about that.

java.lang.NoClassDefFoundError: org/apache/commons/io/filefilter/AgeFileFilter
at net.minecraft.launcher.GameLauncher.cleanOldNatives(GameLauncher.java:327)
at net.minecraft.launcher.GameLauncher.launchGame(GameLauncher.java:175)
at net.minecraft.launcher.GameLauncher.onDownloadJobFinished(GameLauncher.java:497)
at net.minecraft.launcher.updater.download.DownloadJob.startDownloading(DownloadJob.java:75)
at net.minecraft.launcher.Launcher$1.run(Launcher.java:157)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.io.filefilter.AgeFileFilter
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 11 more