I got this when I tried to save my preferences in IE and it tried to open them up in Mozilla (I think)!
[added] although now that I'm looking into I think I might be going mad and mistaken...[/added]
OK, if you go to toolbar options in IE then normally you get taken to the page you were on before you hit options. However, I went to the options on a blank page (no referring page) and the toolbar was supposed to bounce me to googl.com in this instance. But instead something went wrong and I got the error. Probably to do with me messing around with my browsers to make them do better things ;)