An obscure fix to a well-documented problem...
After many months of not using my NTL Webmail account, I discovered that this was "suspended". Tried all the usual stuff -resetting account, password etc. and ringing technical support and got no joy. It turns out that because my account is "pending disconnection" (I am about to move house, hence requirement for webmail) some clever provisioning system had disabled my webmail account (even though everything else, inc my email account was working!). Persistent battering of the poor customer services rep (i.e. refusing to end the call until he re-instated my old account) solved the problem. Hopefully this information will help a fellow NTL-sufferer...
