html: Unexpected call to method or property access

I am trying to use Rounded Corner buttons in my ASP.NET website using AjaxControlToolkit's RoundedCornerExtender. When I use this on a Buton control, I get an error saying "htmlfile: Unexpected call to method or property access" to which I can Break/continue.

When I run the sites, it gives me an error "Unexpected call to mathod or property access".Here's the screensh开发者_StackOverflowot: http://img29.imageshack.us/img29/7051/roundedcornersp.png

Not my are of expertise, but I would guess this does not work on a button control. You could try using a div as button.

Here is the same discussion:
http://forums.asp.net/p/1352765/2766571.aspx

Probably not the answer you're looking for, but is there something wrong with using other purely javascript solutions to rounded corners that are out there?