If this previously worked but after the update it doesn't I would normally say this is firewall related, e.g. blocking avast's web shield. However, I doubt this is the case since you don't report not being able to connect to any web site.
Are you able to browse other sites normally ?
What is your firewall, full name and version, e.g. Zone Alarm Pro/Free version 7.x.x.x, etc.
How do you log-on to the site, normal http page enter user name and password, validated at a secure https web page and finally back to a normal http web page, etc. ?
What browser are you using and have you tried a different browser ?
Does terminating the web shield make any difference ?