This message occurs when you try to use the Java applet for running a PC command on a browser where Java is unavailable. To fix it you must do one of the following:
1) Stop using the Java applet for running PC commands. Use the PC Command Listener instead.
-or-
2) Find a browser that supports Java applets, install the Java plugin and enable applets. (Currently, I think Firefox is the only major browser that still supports Java applets.)