Internet Banking and other secure sites not working anymore.

[Alive]

Hi there everyone,
Just installed AIS on a bunch of clients machines about a month ago, and noticed that one particular machine has stopped running normally. 
Basically an XP SP3 machine, with full updates, since the install has been unable to access Internet Banking, Online Taxation websites, and any thing else with a secure connection. It just times out.
Now I'm not sure why, but it was working fine before, and every other computer on the network with XP, Vista or 7, all with AIS can access the same websites, just not this machine. If Avast is disabled it still wont work, however if uninstalled it does. 
This mostly wouldn't be a problem, but its the accountants machine so its very annoying and time costly to get her to use another machine just to do the banking.
Ive talked with all the various bank's tech support, but to no avail.

So yeah, if anyone has any ideas, would be greatly appreciated.

Alive

[SafeSurf]

The machine is only blocked from these sites or other sites as well.  Have you checked to see if the firewall (FW) is blocking any sites?

What other security software is installed on this machine currently and in the past?

When was the last time an Avast scan was done, and what type was done?

Are the Avast definitions up to date?  Are you using the current version of AIS 5.0.677?

[Alive]

Originally we thought it was only the banking website.  However over a week or so, we found that any sites using a secure connection were blocked.  And no, there is no other security software installed.  It had Norton installed previously.  However i did use the removal tool. 
A scan was completed upon install, and every day at 2am.  Definitions are auto updating and doing so correctly.  Avast is reporting everything as being up to date.
There is nothing in the firewall block list, and the sites are all added to the Internet Explorer trusted sites list.