Checked ListView Count - NullReferenceException

[Zeljko]

Win XP, VS 2008, .NET 2.0

When I use Count property to count checked items in ListView (set to detail view with check boxes), sometimes i get NullReferenceException on count part. Sometimes I get it but sometimes I don't get it... It's very randomly and I can not reproduce it always?!? It just happens sometimes
Can somebody tell me why or point me a lil bit?

CODE:
Private Sub LstVew1_ItemChecked(ByVal sender As System.Object, ByVal e As System.Windows.Forms.ItemCheckedEventArgs) _
Handles LstVew1.ItemChecked
   If LstVew1.CheckedItems.Count > 1 Then
     lbl1.Text = "Selected items: " & LstVew1.CheckedItems.Count
   Else
     lbl1.Text = "U have 1 or 0 selected item(s)"
   End If
End Sub
 
CODE EXCEPTION:
System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Windows.Forms.ListView.CheckedIndexCollection.get_Count()
   at System.Windows.Forms.ListView.CheckedListViewItemCollection.get_Count()
   at ...

Thanks in advance