Found now a solution for me: AxisX.IntervalType, AxisX.Minimum, AxisX.Maximum must match the series DataBindXY(xValues, yValues)
Dim ints as integer = CInt(DateDiff(DateInterval.WeekOfYear, von_X, bis_X, _
FirstDayOfWeek.Monday, FirstWeekOfYear.FirstFullWeek))
Dim xdate(ints) As Date
Dim xInt(ints) As Integer
chart1.ChartAreas("Default").AxisX.IntervalType = DateTimeIntervalType.NotSet
chart1.ChartAreas("Default").AxisX.Interval = 1
chart1.ChartAreas("Default").AxisX.Minimum = 0
chart1.ChartAreas("Default").AxisX.Maximum = ints - 1
chart1.ChartAreas("Default").AxisX.CustomLabels.Clear()
For intVal As Integer = 0 To ints - 1
Dim kw_run As String = ""
kw_run = myClass.set_WeekFormat(myClass.get_WeekNumber(xdate(intVal)), xdate( _
intVal), True)
chart1.ChartAreas("Default").AxisX.CustomLabels.Add(intVal, intVal + 1, kw_run, _
0, LabelMarkStyle.None)
Next
chart1.Series("mySeries").Points.DataBindXY(xInt, yValues)
'...