MP
Connection refused is often either a network issue or the wrong user name and password. Since it is only happening with one site I suspect it is on their end and there is no way to find out.
I would clear the browser cache and cookies
The first step in any troubleshooting is to clear the browser cache/cookies. (you need to clear ALL cookies)
*For Internet Explorer browser & MSN Butterfly: Press CTRL+SHIFT+DEL simultaneously and click Delete
*For Google Chrome: Press CTRL+SHIFT+DEL simultaneously and click Clear Browsing Data
*For Firefox: Press CTRL+SHIFT+DEL simultaneously and click Clear Now
(other browsers are similar)
If clearing the cache doesn't help answer these.
Are you accessing your mail via a web browser or email client? See the differences between them here
Are you having problems accessing other accounts on the same computer?
Does the same problem exist when you use a different browser?
Does the issue persist on other computers?