hi,
This is got to with your firewall/proxy. I have the same problem in work, I have 2 proxies I can go through, I can logon to vodafone on both, I get the popup using one proxy but not on the other. Neither proxy has any popup blockers, and the vodafone popup is the only popup (or indeed site of any nature) Ive ever seen blocked.
I mailed/phoned/complained/escalated to management calls to vodafone fopr help to see what it could be but no avail. Couldnt get anyone to help me. Next to useless tech guys IMO.
I got round it by forwarding all mail to my gmail account and configuring the gmail account to be able to reply using my vodafone address.