Error on delete! with easy appointments

Hi

I have just installed easy appointments, but i am unable to get the email traffic to work. I saw a discussion that you needed an email on the custom page. I had it called customer Email. so I added a new one called Email. I went to delete the Customer Email field but all I get is Error on delete!. I do not want two different email fields.

I have checked and the compatibility mode is clicked. Please could someone help.

thanks Lisa