Error in launching Applet with jre 1.6 update 33 sometimes not always.

Error StackTrace:

java.lang.NullPointerException
at com.sun.javaws.security.SigningInfo.getCommonCodeS ignersForJar(Unknown Source)
at com.sun.javaws.security.SigningInfo.check(Unknown Source)
at com.sun.javaws.LaunchDownload.checkSignedResources Helper(Unknown Source)
at com.sun.javaws.LaunchDownload.checkSignedResources (Unknown Source)
at sun.plugin2.applet.JNLP2Manager.prepareLaunchFile( Unknown Source)
at sun.plugin2.applet.JNLP2Manager.loadJarFiles(Unkno wn Source)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionR unnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)