Java Applet sporadically can't load class in cached jar file due to OverlappingFileLockException. The problem happens while trying to instantiate a new Thread in customer code.

An extract of the jav console log (complete log attached) :

cache: Reading Signers from 3344 https://xxx.com/controls/applets/tctsigned.jar | C:\Users\XXX\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\37\21b17fe5-7d8251a0.idx
network: SyncFileAccess.openLock: handled OverlappingFileLockException, remainint TO : 10000
network: SyncFileAccess.openLock: handled OverlappingFileLockException, remainint TO : 10000
network: SyncFileAccess.openLock: handled OverlappingFileLockException, remainint TO : 9900
network: SyncFileAccess.openLock: handled OverlappingFileLockException, remainint TO : 9800
...
network: SyncFileAccess.openLock: handled OverlappingFileLockException, remainint TO : 300
network: SyncFileAccess.openLock: handled OverlappingFileLockException, remainint TO : 200
network: SyncFileAccess.openLock: handled OverlappingFileLockException, remainint TO : 100
java.io.IOException: handled OverlappingFileLockException, timeout reached
at com.sun.deploy.util.SyncFileAccess.openLockFileObject(Unknown Source)
at com.sun.deploy.util.SyncFileAccess.openLockRandomAccessFile(Unknown Source)
at com.sun.deploy.cache.CacheEntry.openLockIndexFile(Unknown Source)
at com.sun.deploy.cache.CacheEntry.access$000(Unknown Source)
at com.sun.deploy.cache.CacheEntry$10.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.deploy.cache.CacheEntry.readBlock(Unknown Source)
at com.sun.deploy.cache.CacheEntry.readManifest(Unknown Source)
at com.sun.deploy.cache.CacheEntry.getManifest(Unknown Source)
at com.sun.deploy.cache.CachedJarFile.getManifest(Unknown Source)
at com.sun.deploy.security.DeployURLClassPath$JarLoader$2.getManifest(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader$WrapResource.getManifest(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.defineClassHelper(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.access$100(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.plugin2.applet.Plugin2ClassLoader.findClassHelper(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadClass0(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
...
Caused by: java.nio.channels.OverlappingFileLockException
at sun.nio.ch.FileChannelImpl$SharedFileLockTable.checkList(Unknown Source)
at sun.nio.ch.FileChannelImpl$SharedFileLockTable.add(Unknown Source)
at sun.nio.ch.FileChannelImpl.lock(Unknown Source)
... 32 more