Using VC71 compiler and get compiler errors, that i don't understand. Here comes the example

class A
{
public:
  virtual int& myMethod() = 0;
  virtual const int& myMethod()const = 0;
};

class B: public A
{
public:
  // generates: error C3241: 'const int &B::myMethod(void)' : this method was not introduced by 'A'      virtual const int& A::myMethod() const; 
  virtual int&  A::myMethod();
};

when i switch order of both method definitions in B then I see a different compiler error:

class B: public A
{
public:
  virtual const int& A::myMethod() const;
  // error C2556: 'const int &B::myMethod(void)' : overloaded function differs only by return type from 'int &B::myMethod(void)'
  // error C2373: 'B::myMethod' : redefinition; different type modifiers
  virtual int&  A::myMethod();
};

however, if I omit the A:: stuff then i don't get any compiler error:

class B: public A
{
public:
  virtual int&  myMethod();
  virtual const int& myMethod() const;
};

So, what exactly does A:: in front of my method names and why do i see these diverse compiler errors? Any explanation welcome!