Can't start minecraft

===Simple Minecraft Error Test===

Starting Minecraft...

Exception in thread "main" java.lang.SecurityException: SHA1 digest error for

t/minecraft/client/Minecraft.class

        at sun.security.util.ManifestEntryVerifier.verify(Unknown Source)

        at java.util.jar.JarVerifier.processEntry(Unknown Source)

        at java.util.jar.JarVerifier.update(Unknown Source)

        at java.util.jar.JarVerifier$VerifierStream.read(Unknown Source)

        at sun.misc.Resource.getBytes(Unknown Source)

        at java.net.URLClassLoader.defineClass(Unknown Source)

        at java.net.URLClassLoader.access$100(Unknown Source)

        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 sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)

        at java.lang.ClassLoader.loadClass(Unknown Source)

        at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)

Finished session