Error in std::getline function (fstreeam _Lock())

I keep getting an error when call std::getline, the debugger shows a break in a fstream function """virtual void __CLR_OR_THIS_CALL _Lock()"""

Here is my code (Read File function):

string GetFile(const string& fileName)
{
    string line;
    string output;
    ifstream myfile (fileName);
    myfile.open(fileName);//.c_str());

    if (myfile.is_open())
    {
        while ( getline (myfile,line) )
        {
            //cout << line << '\n';
            output.append(line + "\n");
        }
        myfile.close();

    } else cout << "Unable to open file";

    return output;
}

(ADDED)
the break message:

Unhandled exception at 0x7787FC47 (ntdll.dll) in Engine.exe: 0xC0000005: Access violation writing location 0x00000014.

and the break in fstream shows this function:

virtual void __CLR_OR_THIS_CALL _Lock()
    {   // lock file instead of stream buffer
    if (_Myfile)
        _CSTD _lock_file(_Myfile);
    }

I Have no idea what is the problem

It's not an answer but it's a start. I've made a new project and use this code (the same that always):

#define Dir "C:\\difuseVS.txt"

using namespace std;

string GetFile(const string& fileName)
{

string line;
string output;
ifstream myfile(fileName);


if (myfile)
 {

     while ( getline (myfile,line) )
    {
      //cout << line << '\n';
      output.append(line + "\n");
    }
 myfile.close();

}else cout << "Unable to open file"; 

return output;
}

int main()
{
cout << GetFile(Dir);
getchar();

}

And it works perfectly!! the problem is in the project configuration, but I don't know where exactly