Use guest checkout for the time being

New accounts can't currently be created (the database is still partly broken) but orders can be placed using guest checkout. You still pay by Paypal as usual, but will then be returned to an error page when it tries to create an account for you - do not worry, you'll get a Paypal receipt as normal showing you have paid, and your order will have been created. (I'll also email to let you know I received the order but that can be some hours later).

I do intend to take the whole site down to recreate it which will fix this, but it may take some time.