I have a BT Digital Vault account but lately I cannot access the site. I am on 6B Indy 8Mbps and live on Nimanhamin in Chiang Mai.

http://sh.digitalvault.bt.com/

On further testing I cannot even open the main BT website www.bt.com

Both links you provided open without problem on TRUE in BKK.

Have you tried to empty your browser cache and possibly also flush your DNS cache?

There is a problem with the security certificate. It has aparently expired and no one has bothered to pay to renew it. In this case it is I think safe to go to the site ...using the option explorer presented you. I would however consider using another provider though as it does not say much for the secirity of your documents if they cannot pay the few dollars certificate fee.

I flushed my DNS and browser caches, both Chrome and IE and still can't access www.bt.com unless I use my UK VPN server.