C++ :: Error With Multidimensional Vector

I am having trouble accessing a one-dimensional vector as a multi-dimensional one.I have a MultiArray template class, and it is accessed using the function operator. It accesses elements through the expression row * m_columns + col. The row and col are the two inputs to the operator while the m_columns is the width/number of columns in the array. There is also a version that accesses the array with one number. Its underlying representation is a one-dimensional vector.The problem is when I try to load a level:

void Map::LoadFromFile(const std::string& filename) {
std::ifstream map_file(filename);
std::cout << m_map.GetHeight() << ", " << m_map.GetWidth() << std::endl;
std::cout << m_map_dimensions.y << ", " << m_map_dimensions.x << std::endl;
if(map_file.is_open())

[code].....