ORA-35572

hi every one

I am creating a cube . it forces me to select two PK which I don't understand why I have one main PK.

I have one main PK and map into member and create one level above that maps to parent now facing this issue

ORA-35572

can anyone assist?

I also have two more question :

1: If I have just one level is it still mandatory to create level and Hierarchy?

2:what is difference between different roles? should any of them be prefered?

thanks