Reference to pointers and C++ polymorphism

does anyone know why this gives a compiler error ? I tried VS 2005 and Codewarrior:

class Parent {
   protected:
      int m_Var;
   public:
      Parent() : m_Var(0) {}
      virtual ~Parent() {}
      void PubFunc();
};

class Child : public Parent {
   protected:
      bool m_Bool;
   public:
      Child() : m_Bool(false) {}
      virtual ~Child() {}
      void ChildFunc();
};

void RemoveObj(Parent *& ppObj)
{
   delete ppObj;
   ppObj = 0;
}

int main()
{
   Parent* pPObj = 0;
   Child*  pCObj = 0;
   pPObj = new Parent();
   pCObj = new Child();

   RemoveObj(pPObj);
   RemoveObj(pCObj);
   return 1;
}

Visual studio says:

refptr.cpp(33) : error C2664: 'RemoveObj' : cannot convert parameter 1 from 'Child *' to 'Parent *&'

Thanks