illegal choice

Wow, how is that headline for a bunch of Drupal gobbledygook jargon?

To break it down, I have a content type with a cck user reference field.

That field's options are populated by the results of a view.

That view builds a list of users who belong to the same Organic group as the active user. It has a argument that supplies the user's group by default. That works fine because users can only belong to one group on this site.

But anonymous users don't belong to groups, so no results are returned.