My apologies if a thread such as this already exists, but I couldn't find one.

I'm creating a custom follower and everything is working fine except for the relationship tab. I right click in the list, select new, and the window comes up, but it won't allow me to select my follower as the parent npc.

Any ideas?

Is your follower unique? NPCs in relationships must be unique. That's the first thing that usually trips people up on that.