I tried clearing cache/browsing data, using two different browsers. Also clicking both forgotten password and email options. Then tried the 'Find your username' section, filled in my details and just got "This part of the site isn't working at the moment, but it'll be up and running again soon" which seems to have been that way for a while.
Check your account settings and under INCOMING MAIL SERVER Username check that matches your expected username for no apparent reason my username did not have "@virgin.net" on the end and when i did that marked the Account active again it verified and worked!
I was getting an Error "Cannot Get Mail" The username or password for "<my correct username> is incorrect. Resetting the password had no effect. Both the username and password were correct, but the username in INCOMMING MAIL SEERVER had lost the domain name inexplicably.
Same problem for me. Says both my username and password (that previously worked) are not recognised. If I try to re-register or the "Find my username" options I just get the 'Oops, something's broken' error..