First things first - check that all the details you've used to register are correct. If you've found an error then we'll need some documents from you to update your details - have a look here.
No typos? All looks good?
In that case, it could just be that the sources we have out-of-date information which could be due to:
a recent change in address
a recent change in name (due to marriage or deed poll)
Don't worry, you'll just need to upload your documents and our lovely verification team will manually verify your account.