Maybe there is something that I don't understand. I've created a database with all of the relationships () but when I go into LLBLGen Pro I am not able to create sub-types or super-types. One is created automatically on the 1:1 relationship but now I'm not able to even manually on any of the other relationships.

What am I missing?

They have to be 1:1 and joined using PKs. What type of relationships are you not able to use for inheritance?