Access Violation with helper functions

[Lang]

I have class A trying to access helper functions in class B.

class A has a friend class B declaration and vice verse.

However when class B tries to use the helper function I get an access violation.

class A{
     friend B;
     private:
            string a;

     public:
            string returnString(){ return a; }
};

Can anyone tell me what's wrong with that?

Thanks,
Lang