Add refrence of 1 class libaray into another class libaray?

 How we can add reference of a class library into another class library ? i know about using "Add Reference"  we can add the reference of a 1 class libaray name into another project. But i want to know any other ways because on compile time i am getting error of "Missing directive or assembly reference " .  Is there any other way to add assembly reference? IF yes, then plz help me in that thing