Not really. I really don't claim to be a shipping expert

I would check that you have the 'walk in' option activated.

Other Options storepickup

That is the default one that is going to be used if there is nothing else available. Maybe you are getting a blank screen because there are no available options.

Do you mean it goes to a blank screen when you create the user account? Or do you mean it goes to a blank screen when that user tries to check out? If it is the second of the two between which pages does it go blank?