“Sure you want to do this?” error updating theme

Whenever I try to update anything in Theme Design mode, I get a message that says “are your sure you want tot do this?”. I always click Yes, and it takes me back to the edit page, but the changes have not been made. I’m trying to edit some of the widgets, but it won’t let me.

I also want to change the theme, and edit the sidebars, and it won’t let me do that either. It’s only one site that does this, all the others are find. Anyone know how I can get around this?? I really need to edit that thing!

Thanks very much.