No matching function for call to unresolved overloaded function type

I am getting an error which I don't understand. I'm sure it is quite simple.. but I am still learning C++. I'm not sure if it is related to my parameters being exactly the same for the pure virtual function declaration or if it is something else.

Here is my simplified code:

in header_A.h

class HandlerType
{
public:
   virtual void Rxmsg(same parameters) = 0; //pure virtual
};

--------------------------------------------------
in header_B.h

class mine : public HandlerType
{
public:
   virtual void myinit();
   void Rxmsg(same parameters); // here I have the same parameter list 
//except I have to fully qualify the types since I'm not in the same namespace
};

--------------------------------------------------
in header_C.h

class localnode
{
public:
virtual bool RegisterHandler(int n, HandlerType & handler);
};
--------------------------------------------------

in B.cpp

using mine;

void mine::myinit()
{
   RegisterHandler(123, Rxmsg); //this is where I am getting the error
}

void Rxmsg(same parameters)
{
   do something;
}