I'm having the same problem as the login doesn't recognise my mother's maiden name either. I thought surely I would know my mother's maiden name but I was beginning to doubt if I had put the correct one down! I also rang Essex and was told there was a problem with it recognising the mother's maiden name so they couldn't send out reminders of passwords. I'm still waiting for that email and it's torture!
I had this problem two weks ago and rung up to find out why I could not log on. The lady re-set my details and emailed me a password and then I could get in. It is case sensitive as well which proved difficult at the time, she informed me of what my password was and how exactly I had typed out my email address (all capitals etc) so it may be worth having a go at typing in different ways.