It appears you want to send a pointer to a CString. Wrong: SendMessage(hMain, WM_SEND_HELLO, 0, (LPARAM &) text); Right: SendMessage(hMain, WM_SEND_HELLO, 0, (LPARAM) &text); Personly I recommend sending the address of the string instead of the address of a CString object. SendMessage(hMain, WM_SEND_HELLO, 0, (LPARAM)(LPCSTR)text); Trust in the code Luke. Yea right!