code :

Private Sub f_findwindow()
Dim hwnd1
hwnd1 = findwindow("windowname", "")
w_setfocus
End Sub
Private Sub w_setfocus()
Dim rtn As Long
Dim hwnd1
rtn = setfocus(hwnd1.hwnd)
End Sub

module :
Public Declare Function findwindow Lib "user32" Alias "findwindowa" _
(ByVal lpclassname As String, ByVal lpwindowname As String) As Long

Public Declare Function setfocus Lib "user32" (ByVal hwnd As Long) As Long

occur '453' runtime error
help me