non-static reference member 'A& B::myA', can't use default assignment operator

Example.cpp

#include <iostream>
#include <vector>
using namespace std;

class A; //Forward declaration

class B{
	public:
		B(string name, A& a):myA(a), name(name){
			cout << "Works with pointer" << endl;
		};
	private:
		A& myA;
		string name;

};

class A{
	public:
		A(){
			cout << "Constructing A" << endl;
			if(bs.empty()) cout << "Vector is empty" << endl;
			bs.push_back(B("First", *this));
			cout << "Array has " << bs.size() << " elements." << endl;
		};
	private:
		std::vector<B> bs;
};


int main() {
	cout << "Start" << endl;
	A a;
	cout << "Ok." << endl;
	return 0;
}

make all
Building file: ../src/ConstructorExample.cpp
Invoking: GCC C++ Compiler
g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/ConstructorExample.d" -MT"src/ConstructorExample.d" -o "src/ConstructorExample.o" "../src/ConstructorExample.cpp"
../src/ConstructorExample.cpp: In member function 'B& B::operator=(const B&)':
../src/ConstructorExample.cpp:7: instantiated from 'void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = B, _Alloc = std::allocator]'
/usr/include/c++/4.2.1/bits/stl_vector.h:608: instantiated from 'void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = B, _Alloc = std::allocator]'
../src/ConstructorExample.cpp:23: instantiated from here
../src/ConstructorExample.cpp:7: error: non-static reference member 'A& B::myA', can't use default assignment operator
/usr/include/c++/4.2.1/bits/vector.tcc: In member function 'void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = B, _Alloc = std::allocator]':
/usr/include/c++/4.2.1/bits/stl_vector.h:608: instantiated from 'void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = B, _Alloc = std::allocator]'
../src/ConstructorExample.cpp:23: instantiated from here
/usr/include/c++/4.2.1/bits/vector.tcc:256: note: synthesized method 'B& B::operator=(const B&)' first required here
make: *** [src/ConstructorExample.o] Error 1

**** Build Finished ****