I have an iOS app where users can save contacts. There is a minimum of first name and last name to save, so when they try to save without filled out all the required fields, an alerts pops up that says. "Error: Not all required fields are filled out. If you continue, your contact will be lost. Do you want to continue?" If they hit yes, their new contact is discarded and the data is lost. If they hit no, they can continue filling out the fields. This is very confusing, but I cannot think of a better way to phrase the error, or use different button text. Does anyone have a better idea?
The best way is to not show any error at all and try to figure something from users input: if you will try to enter a phone number only at a standard iOS address book new contact screen it will proceed without any confirmation and this is OK since it's my own decision to not name the contact (anyway, I can change it later): phone number will be used as a title in the contacts list.
And if you still prefer to keep the error, it should sound like this: "First name or Surname is not entered. Proceed anyway?", i.e. it's better to not frighten your users but kindly remind of missing fields and let user do that she wants (continue without entering name).