Cannot reply to a specific email message

Cannot reply to a specific email message

I've recently opened a Zoho mailbox.
So far I've received 3 mails.
With 2 of them I had no problems, but to one of them I cannot reply.
When I click reply, the blue "loading" message appears for 0.1s to 0.5s, then it disappears and nothing else happens.
I'm using FF 3.0.10, but it also happens on my IE 6...

What should I do?

Thanks...