Hi again,
I am using Peter Beache's code as follows to test if there is another
instance running but I don't know how to close it if it is


You can send a WM_CLOSE message to the hWnd in question.
See modified code below.

Regards,
Vic Eldridge



Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
(ByVal lpClassName As String, _
lpWindowName As Any) As Long
Private Declare Function GetNextWindow Lib "user32" Alias "GetWindow" _
(ByVal hwnd As Long, _
ByVal wFlag As Long) As Long
Private Declare Function GetClassName Lib "user32" Alias "GetClassNameA" _
(ByVal hwnd As Long, _
ByVal lpClassName As String, _
ByVal nMaxCount As Long) As Long
Private Declare Function PostMessage Lib "user32" Alias "PostMessageA" _
(ByVal hwnd As Long, _
ByVal wMsg As Long, _
ByVal wParam As Long, _
ByVal lParam As Long) As Long

Private Const GW_HWNDNEXT = 2
Private Const WM_CLOSE = &H10

Sub DupeXLRunning()
Dim lRet&
Dim StrRet$
Dim nLen&

lRet& = FindWindow("XLMain", ByVal 0&)

' Now this will always return a valid HWND,
' being the handle of this instance of XL

Do
lRet& = GetNextWindow(lRet&, GW_HWNDNEXT)
If lRet& = 0 Then Exit Do
StrRet$ = Space$(100)
nLen& = GetClassName(lRet&, StrRet$, 100)
StrRet$ = Left$(StrRet$, nLen&)
If UCase$(StrRet$) = "XLMAIN" Then
MsgBox "Duplicate version of XL found."
PostMessage lRet&, WM_CLOSE, 0&, 0&
Exit Sub
End If
Loop
MsgBox "Only one version of XL running"
End Sub