Not polymorphic query

[sono-un-as...@libero.it]

Hi Guys,   
(In Cayenne 2.0 version) Considering the hierarchical class tree to single 
table example, if I perform this kind of not-polymorphic query:    
  
SelectQuery query = new SelectQuery( Manager.class );  
  
I receive this error : "No inheritance - there must be only one override 
set"   
It's my error or I can't do a not-polymorphic query at all?   
__  
Domenico