Issues with constructors for nested class of a template (copy ctor seems to override other ctor)

I have a homework assignment to do a template class of a Matrix, which includes some pretty basic and simple stuff. We also need to create a forward iterator class for it (a nested one) which behaves in a standard way, it should specifically support a copy constructor.

Here is the relevant matrix.h code:

template<class T>
class Matrix
{
public:
    //nested iterator class
    class iterator
    {

    public:
        typedef iterator self_type;
        typedef T value_type;
        typedef T& reference;
        typedef T* pointer;
        typedef std::vector<T>& vector;

        iterator(Matrix &other, int index) :
            _currIndex(index), _currMatrix(other)
        {

        }

        iterator(iterator& other) :
            _currIndex(other._currIndex), _currMatrix(other._currMatrix)
        {

        }
    private:
        int _currIndex;
        Matrix<T>& _currMatrix;
    }

    //function that creates an iterator for the current matrix
    iterator begin()
    {
        return iterator(*this, 0);
    }

    iterator end()
    {
        return iterator(*this, _data.size());
    }

private:
    unsigned int _rows;
    unsigned int _cols;
    vector<T> _data;
}

Matrix has several constructors like copy, empty etc. They initialize the private members and nothing else. The iterator class also overloads the ++ operator

The problem I'm facing is with compiling the following code in Linux using g++:

for(auto it = m.begin(); it != m.end(); it++)
{
    cout << *it;
}

On windows, in Visual Studio the code compiles and runs OK with no issues. On linux, when compiling the following error pops up:

debug.cpp: In function ‘int main()’:
debug.cpp:63:24: error: no matching function for call to ‘Matrix<int>::iterator::iterator(Matrix<int>::iterator)’
  for (auto it = m.begin(); it != m.end(); it++)
                        ^
debug.cpp:63:24: note: candidates are:
In file included from debug.cpp:11:0:
matrix.h:35:3: note: Matrix<T>::iterator::iterator(Matrix<T>::iterator&) [with T = int]
   iterator(iterator& other) :
   ^
matrix.h:35:3: note:   no known conversion for argument 1 from ‘Matrix<int>::iterator’ to ‘Matrix<int>::iterator&’
matrix.h:29:3: note: Matrix<T>::iterator::iterator(Matrix<T>, int) [with T = int]
   iterator(Matrix other, int index) :
   ^
matrix.h:29:3: note:   candidate expects 2 arguments, 1 provided

If I comment out the copy constructor for the iterator class, then the code compiles fine on Linux (and windows). If I keep both constructors, then g++ throws the error. Its as if the copy constructor is overriding the previous constructor and I have no idea why.

Can anyone share some insight as to why this is happening? maybe how I can fix it?