Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
  (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
 
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
  (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
  lParam As Any) As Long

Const WM_SYSCOMMAND = &H112
Const SC_CLOSE = &HF060
Const LNULL = 0&
 
Dim hWnd As Long
hWnd = FindWindow(vbNullString, "Exakter Fenstertitel")
If hWnd <> 0 Then
  SendMessage hwnd, WM_SYSCOMMAND, SC_CLOSE, LNULL
End If