Hi Nicolas,
"First, this can happen if you unpublished some of the default custom address fields via the menu Display->Custom fields while still having the "No address" option of the PayPal plugin turned off. So either publish the fields back or turn on that option. Also, sometimes, changing the "address override" option of the PayPal plugin's options can solve the problem."
I didn't unpublish anything -- and I am a little confused. I can not recreate the problem so I will have to contact the customer and have them try again to test once the settings are right. I have attached a screen shot. Can you take a look and let me know if you think they're correct?
Thanks for your fast reply!