Hi Richard,
In another thread some time ago i found that VLookup() produces a
runtime error when the value can not be found. You can use the
following to snap that event.
Code:

On Error Resume Next

'VLookUp()

If Err.Number < 0 Then
'If not found
Debug.Print Err.Number
Debug.Print Err.Description
Else
' If found
End If
On Error Goto ErorrHndl

Regards,
Bondi