Error with 'ostream' and 'istream' in C++ trying to overloading

When modifying a TAD withtemplates to make it generic (add templates):

For input / output data I have this code:

std::ostream& operator<<(std::ostream& os, Matrix & m)
{
  os << m.rows() << " " << m.columns() << std::endl;
  os << std::setprecision(4) << std::fixed;
  for(int i=1; i <= m.rows(); i++)
  {
    for(int j=1; j <= m.columns(); j++)
    {
      os << m.value(i,j) << " ";
    }
    os << std::endl;
  }

  return os;
}

std::istream& operator>>(std::istream& is, Matrix& m)
{
  int rows, columns;
  float v;

  is >> rows >> columns;
  for (int i=1; i<=rows; i++)
  {
    for (int j=1; j<=columns; j++)
    {
      is >> v;
      m.assign(i,j,v);
    }
  }

  return is;
}

The definition (summary):

#ifndef MATRIX_HPP
#define MATRIX_HPP

#include <stdexcept>
#include <iostream>
#include <iomanip>

template<typename E, int R, int C>
class Matriz
{
public:
  Matrix();
private:
  E elements_[R][C];
};
#include "matrix.cpp"
#include "matrix_io.cpp"

#endif // MATRIX_HPP

The implementation (summary):

#include <limits>
#include <cmath>

template<typename E, int R, int C>
Matrix<E,R,C>::Matrix()
{
  for(int i=0; i<R; i++)
  {
    for(int j=0; j<C; j++)
    {
      elements_[i][j] = 0; 
    }
  }
}

Here is the error:

#include "matrix.hpp"

#define Element float

#define MatrixP Matrix<Element, 3, 3>

void tryBuildMatrix()
{
  MatrixP m;
  std::cout << m;
}

This error:

error: cannot bind 'std::ostream {aka std::basic_ostream}' lvalue to 'std::basic_ostream&&' std::cout << m;

Any idea why it occurs?

PS: if I remove the template the code is perfect.