Same problem here!
Worked fine until i installed Opera 9. Same problem in WinXp Opera, GNU/Gentoo Opera,Firefox and OSX Opera,Safari.
Presume its Java relateed, but how do we fix it? Or is it an issue for WP dev?
Ive got the same problem:
http://overmoen.no-ip.info/~hula/
gives the exact same error….
The first thing i added to the sidebar was a text widget, and got that error. I use the widget sidebar now, but i would like to edit the widgets, and add a text field. 🙂
