Private Declare Function CreateMutex Lib "kernel32" Alias "CreateMutexA" ( _
ByRef lpMutexAttributes As Any, _
ByVal bInitialOwner As Long, _
ByVal lpName As String) As Long


Private Declare Function ReleaseMutex Lib "kernel32" ( _
ByVal hMutex As Long) As Long


Private Declare Function OpenMutex Lib "kernel32" Alias "OpenMutexA" ( _
ByVal dwDesiredAccess As Long, _
ByVal bInheritHandle As Long, _
ByVal lpName As String) As Long

Private Declare Function CloseHandle Lib "kernel32" ( _
ByVal hObject As Long) As Long



Private Const ERROR_ALREADY_EXISTS = 183&

Private Const MUTEX_ALL_ACCESS = &H1F0001

Private lngMutex As Long



Sub Auto_Open()

lngMutex = OpenMutex(MUTEX_ALL_ACCESS, 0, "Test Mutex")

If lngMutex = 0 Then

lngMutex = CreateMutex(ByVal 0, 0, "Test Mutex")

Else

Call CloseHandle(lngMutex)

Call MsgBox("The App is running already")

End If

End Sub



Sub Auto_Close()

Call ReleaseMutex(lngMutex)

End Sub