MsgBox is making the code hang

[simora]

I have a worksheet change event that fires if a specific condition exists.
[cells to the left are blank ]
I want to tell the User to post data to those cells first, but my MsgBox is making the code hang.
Any ideas.

Private Sub Worksheet_Change(ByVal Target As Range)

If Target.Offset(-4, 0).Value = "" Or Target.Offset(-7, 0).Value = "" Then
    Target.Value = ""
    MsgBox " POST THE DOC FIRST "
    Exit Sub
End If
End Sub