Only One Account Won't Send Email

I use WLM for two POP3 accounts and one HTTP account. All accounts have
received and sent mail without a problem until yesterday when all of a
sudden one of the POP3 accounts will not send any mail. It still receives
mail, but whenever I try to send mail (new, reply, or forward) an error
message immediately pops up:

"Your server has unexpectedly terminated the connection. Possible causes for
this include server problems, network problems, or a long period of
inactivity. Windows Live Mail Error ID: 0x800CCCOF"

Why would this account stop sending email? I've changed nothing on this
computer at all.

Any ideas?

--

Bob