I can see it's not just me who has issues with this. I have sent this issue to the support team and never got any answer (Re: (Case 116721) xceed chart for asp.net).
This issue is only for Firefox, I did not find it in IE of any kind.
Anyway, if you replace or to add the <script LANGUAGE = "JScript"> the type tag: like this: type="text/javascript" that stops giving the error. For the developers it will be a very simple fix.
The the Xceed people: >>>> Please fix this.