I am using my girlfriends work email as I do not have a pay email address. We do not have an address from our ISP (Verizon) and my work email is only available when I'm at work (I work on ships and am currently on leave). The above email is from her job as a magazine Editor. I waited for four days before receiving the 'invalid email address' message.
This would most likely be because you are using an email from an apparently private domain which isn't an administrator account and so opens itself up to multis.
To me the easiest solution would be to reregister using your work email account (when you can get back to it) to get the password and then change th email account that you use to receive combine messages.
Thanks for the advice but unfortunately (or fortunately!) I won't be back to work until January and when I do go back I won't have the internet (apart from emails) for four months! I thought that I could use her work email and still be within guidelines of the site - is it because it is in her name and not mine?