Iterate trough std::map

My program crashes when I iterate through a std::map. m_pTextureLoader is a pointer to an object that loads textures (the file names) from directories and stores them in a std::map. The key in the map is the directory of the loaded texture and the second, a std::vector, contains strings for every available texture in that directory. The texture loader has a function that returns a pointer to the texture map. When I iterate through the map, the program crashes when it reaches it++ (which is after the first directory).

typedef std::map<std::string, std::vector<std::string> >	TEXTUREFILENAMES;

m_pTextureFileNames = m_pTextureLoader->GetTextureFileNames();

//for each directory

for(TEXTUREFILENAMES::const_iterator it = m_pTextureFileNames->begin(); it != m_pTextureFileNames->end(); it++)
{
//for each texture

for(DWORD c = 0, d = 0; d < it->second.size(); c++, d++)
{
//Do something

}
}