C++ C2676 error when using "+" to appened 2 strings - c++-cli

Question

Error C2676 binary '+': 'std::string' does not define this operator or a conversion to a type acceptable to the predefined operator
I am getting the C2676 error when trying to append two strings. I have tried everything I can think of, but no luck.
The include and using code is as follows.
#pragma once
#include <string>
#include <iostream>
#include <windows.h>
#include <stdlib.h>
#include <tchar.h>
#include <stream>
#include <cstdlib>
#include <conio.h>
//#include <winnt.h>
//#include <WinUser.h>
using namespace std;
using std::string;
using std::wstring;
namespace CppCLRWinformsProjekt {
using namespace System;
using namespace System::ComponentModel;
using namespace System::Collections;
using namespace System::Windows::Forms;
using namespace System::Data;
using namespace System::Drawing;
using namespace std;
The code that is giving me trouble is.
private: System::Void bntSelected_Click(System::Object^ sender, System::EventArgs^ e) {
int numSelected = this->checkedListBox1->CheckedItems->Count;
if (numSelected != 0)
{
// Set input focus to the list box.
//SetFocus(lstReceiver);
string s = "";
// If so, loop through all checked items and print results.
for (int x = 0; x < numSelected; x++)
{
// it appears that the first "+" sign is what is giving me trouble
s = s + lstReceiver + (x + 1).ToString() + " = " + this->checkedListBox1->CheckedItems[x]->ToString() + "\n";
}
this.lstReceiver.Items.Add(s);
}