Give this a try -
BOOL CMyRichEditCtrl::PreTranslateMessage(MSG* pMsg)
{
// TODO: Add your specialized code here and/or call the base class
if (pMsg->message == WM_KEYDOWN && pMsg->wParam == 0x58 && (::GetKeyState(VK_CONTROL) & 0x8000) != 0)
{
if (AfxMessageBox(_T("Delete Text?"), MB_YESNO) == IDYES)
PostMessage(WM_CUT);
return TRUE;
}
return CRichEditCtrl::PreTranslateMessage(pMsg);
}