C# COM DLL cannot set the callback of MFC's function

]
delegate bool CallBack(int hwnd, int lParam);

class CMyDlg : public CDialog
{

Init()
{
    cpi = NULL;
    CoInitialize(NULL);
    HRESULT hr = CoCreateInstance(CLSID_InterfaceImplementation,
        NULL, CLSCTX_INPROC_SERVER,
        IID_IManagedInterface, (LPVOID*)&cpi);
    retval = 0;
    if (FAILED(hr))
    {
        printf("Couldn't create the instance!... 0x%x\n", hr);
    }
    else
    {
        CallBack^ myCallBack = gcnew CallBack(&Report);
        cpi->SetCallback( myCallBack );
    }
}

static bool Report(int hwnd, int lParam)
    {
       return true;
    }
}    ;

namespace DLL_COM_TEST
{
    public delegate bool CallBack(int hwnd, int lParam);

    public interface IDLL_COM_TESTInterface
    {
        void Execute();
        void SetCallback(CallBack funcCB);
    }
    
    public class IDLL_COM_TESTImplementation: IDLL_COM_TESTInterface
    {
        CallBack funcCB_E;
        public void SetCallback(CallBack funcCB)
        {
            funcCB_E = funcCB;
        }
        public void Execute()
        {
             funcCB_E(1111, 1);
         }
    }

error C3756: 'CallBack': Definition of delegate will conflict with existing symbol .
Please check 'CallBack' 
'myCallBack' is not defined
error C2061: error 'CallBack'
error C2065: 'myCallBack' : is not defined