Range of vba auto_open method when applied to object

After a few days ago a written list of vba, the requirement is open a excel worksheets will automatically perform, I write the code as follows:

 Private Sub Auto_Open () 
Dim Obj As Object, sn As String 
For Each Obj In GetObject (" WinMgmts: "). InstancesOf (" Win32_BaseBoard ") 
Sn=Obj. SerialNumber 
Next 

If the Range (" A24 ")="NC program name" Then 
If sn="K716333294" Then 
Call the Work 
The Else 
MsgBox "equipment authentication failed!" 
End the If 
End the If 
End Sub

` ` `
I put it in add-in, such errors: method range ACTS on the object _global failed
Points to the

 If the Range (" A24 ")="NC program name" Then

I suspect the macro when run automatically, excel spreadsheet is not finished loading,
Can you tell me bosses how to solve