Firstly, this can be caused by being behind a proxy server. The most likely explanation for this would be using a shared computer, and if you don’t have administrative there is nothing you can do about it.
Secondly, ensure that Java is running effectively on your machine. This process differs slightly depending on which browser you are using. For Internet Explorer, firstly, click ‘Tools’ and then ‘Internet Options’, and then select the ‘Security’ tab, and the ‘Custom Level’ button.
Next scroll down to ‘Scripting of Java applets’, and ensure that the ‘Enable radio button’ is selected, before selecting OK to approve your preference.
For Google Chrome click the icon in the top-right corner of Chrome which is shaped like a gear, and then select ‘Settings’. Next select the option ‘Show advanced settings’, and under the ‘Privacy’ section, click ‘Content Settings’.
For Opera, firstly click the Opera drop-down menu which is located in the top-left corner of the Opera browser. Next select Settings > Preferences, or if you’d prefer to use a shortcut then you can also press CTRL + F12 simultaneously to bring up the Preferences screen.