There was a period of time when we had the ActiveX plugin up online signed with the older certificate. If you re-download the ActiveX plugin from our website and re-install it you should be good to go. You may need to clear your Java cache on the client machines affected to ensure that the new plugin gets downloaded.
What version of Java do you have? Not only did you need the right version of the all plugins, you need a later version of Java on the client machine. Try upgrading to the latest and try launching again.
I’m not sure exactly what version it was where they altered the jar signing stuff. I know that 6u4 is too old. I think it was somewhere between 6u10 and 6u13. In any case, there are good security reasons to upgrade to 6u20 or later, so it might be a good idea to go upgrade your clients version of java anyhow.