Java issues with Heatmap under vOPS 6.3?

It seems I'm battling to get the heat map working in 6.3. I'm using firefox 18.0.1 and I've approved the java applet to run whenever I connect to the vOPS site. However every time it launches I get a page error. Looking at the java console it is telling me the following ( I have edited out the domain name):

network: Cache entry not found [url: http://vops.xxxxx.com/, version: null]

network: Cache entry not found [url: http://vops.xxxxx.com/com/labescape/explorer/applet/HeatMapExplorerApplet.class, version: null]

network: Connecting http://vops.xxxxx.com/com/labescape/explorer/applet/HeatMapExplorerApplet.class with proxy=DIRECT

network: Connecting http://vops.xxxxx.com:80/ with proxy=DIRECT

network: Cache entry not found [url: http://vops.xxxxx.com/com/labescape/explorer/applet/HeatMapExplorerApplet/class.class, version: null]

network: Connecting http://vops.xxxxx.com/com/labescape/explorer/applet/HeatMapExplorerApplet/class.class with proxy=DIRECT

network: Connecting http://vops.xxxxx.com:80/ with proxy=DIRECT

java.lang.ClassNotFoundException: com.labescape.explorer.applet.HeatMapExplorerApplet.class

          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)

          at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)

          at sun.plugin2.applet.Plugin2Manager.initAppletAdapter(Unknown Source)

          at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)

          at java.lang.Thread.run(Unknown Source)

basic: load: class com.labescape.explorer.applet.HeatMapExplorerApplet.class not found.