The field(s) that normally show within the 'Account Information' block on the new order page (on then admin side) have stopped showing and I'm not sure why, this is when I make new customer whilst adding the order. Specifically the email address field, most important because I can't add the order without it.
To get around this issue I'm creating the customer first separately, before then adding the order - Any ideas? I'm well and truly stuck with this one
You should check your custom admin template pages . The best way you try to enable Template Path Hint for admin template pages. I think you customized some template pages that caused your issue now.
Quick guide: you should check: