Rob,
Has an instance of ptprofile been created with the association set to the instance of encounter that you are displaying on your page? If not, you'll need to create that object and make sure to associate it to the encounter object that is displayed on your page.
Btw, 1 - 1 relationships mean just that. Each ptprofile can be associated with only 1 encounter and each encounter can be associated with only 1 ptprofile. In my experience, 1 - 1 associations are rare in Mendix development....just want to make sure you realized how they work.
Mike