The most likely cause is a problem with Java on your system - older and/or messed up Java installations seems to cause this issue sometimes. To fix: Step 1: Try installing latest Java version. Check your Firefox/system browser plugins from this page, and install latest version: [http://www.mozilla.com/en-US/plugincheck/ Mozilla Plugin Check Page] (also works for most other browsers) If latest Java (currently "Java(TM) Platform SE 6 U20 - Next Generation Java Plug-in 1.6.0_20 for Mozilla browsers") does not fix the problem, you may have more versions installed on your system causing problems for each other. This leads us to - Step 2: Uninstall those you can from Control Panel -> Add/Remove programs. To make sure it is properly cleaned out, see [https://support.mozilla.com/en-US/forum/1/595817#threadId608043 these excellent tips from noah_sumo] to clean out Java completely, then install latest version again from the [http://www.java.com/en/download/manual.jsp Java.com download page]. If you ''still'' get this error, you may have Norton or another security program which can also in some cases cause this issue. That takes us to: Step 3: Configure security program correctly. For Norton 360 see [[Configuring Norton 360]]. For Norton Internet Security, see [[Configuring Norton Internet Security]]. For other firewall programs, see [[Firewalls]]. If none of these steps solves the problem, please provide any detail you can think of that may be related and let us know, and we will try to find other solutions to get this solved.

Thanks for this, I have managed to install the latest FF version and am updating Java so will see what happens after that. Thanks again