There are frequently cache corrupting problem with Java 7.
The problem occur only with an applet in IE (currently).
Not see it with Java Web Start or with Firefox.

Here are one typical thread dump. More details are in the attched console logs.
 
OS: XP and Vista
Browser: IE8 and IE9 beta
Java: 1.7.0_111, and 1.7.0_100


java.lang.RuntimeException: ERROR: Failed to recover corrupt cache entry
                at com.sun.deploy.cache.CacheEntry.recover(Unknown Source)
                at com.sun.deploy.cache.CacheEntry.getManifest(Unknown Source)
                at com.sun.deploy.cache.CachedJarFile.getManifest(Unknown Source)
                at com.inet.helpdesk.loader.AsynURLClassLoader.definePackage(AsynURLClassLoader.java:414)
                at com.inet.helpdesk.loader.AsynURLClassLoader.defineClass(AsynURLClassLoader.java:388)
                at com.inet.helpdesk.loader.AsynURLClassLoader.findClass(AsynURLClassLoader.java:231)
                at java.lang.ClassLoader.loadClass(Unknown Source)
                at java.lang.ClassLoader.loadClass(Unknown Source)
                at java.lang.Class.forName0(Native Method)
                at java.lang.Class.forName(Unknown Source)
                at HelpDesk.init(HelpDesk.java:47)
                at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
                at java.lang.Thread.run(Unknown Source)