Sub cmdFilterOpenCalls_Click()
Dim t1, t2 As String
On Error Resume Next
    t2 = ActiveCell.Address
    t1 = AutoFilter.Filters.Item(3).Criteria1 ' löst einen Fehler aus
    If Err.Number <> 91 Then Selection.AutoFilter   ' switch filters off
    If Err.Number = 91 Then                         ' no autofilter is applied
        Selection.AutoFilter Field:=3, Criteria1:="<>*close*", Operator:=xlAnd
    ElseIf t1 = "" Then                             ' autofilter for column 3 
    ' is empty
        Selection.AutoFilter  Field:=3, Criteria1:="<>*close*", Operator:=xlAnd
    Else                                            ' switch autofilter on
        Selection.AutoFilter
    End If
End Sub