If the email address you wish to remove has a (C) or a ( next to it, this means it's still set as the Contact (C) or Billing ( contact for your account. In cases like this you would have to update your contact address or update the billing address before being able to delete it.
Frankie P. Community & Social Media Support
Did I answer your question? If so, please mark my post as an "Accepted Solution" by clicking the Accept as Solution button in the bottom right hand corner of this post.