Unable to type for sending mail

I faced the problem today only.When I tried to reply a mail the page opens with an error, the box where we type didn't open at all. Except that everything was o.k. I use IE-7. This is not happening with other mails.I tried Rediff and found working.I tried to clear cache ,history etc.. but no result.
Can any body help me where the settings have been changed. It worked fine with other browsers.