MSChart DateTime only shown as OLE-Automation

I have 3 ChartAreas in 1 Chart each is initalized the same way (only other names). Each ChartArea has its own Series (still initialized the same way) which are filled as follows:

DateTime Datum = Pair.Key;
                     if (Datum1_gewählt.Contains(Datum))
                     {
                         foreach (Tuple<DateTime, int> t in Pair.Value)
                         {
                             //Füge Messwert mit Zeit der aufzeichnung hinzu
                             mySeriesHRM1.Points.AddXY(t.Item1, t.Item2);
                         }
                     }
                     if (Datum2_gewählt.Contains(Datum))
                     {
                         foreach (Tuple<DateTime, int> t in Pair.Value)
                         {
                             //Füge Messwert mit Zeit der aufzeichnung hinzu
                             DataPoint pt = new DataPoint(t.Item1, t.Item2);
                             mySeriesHRM2.Points.Add(pt);
                         }
                     }
                     if (Datum3_gewählt.Contains(Datum))
                     {
                         foreach (Tuple<DateTime, int> t in Pair.Value)
                         {
                             //Füge Messwert mit Zeit der aufzeichnung hinzu
                             mySeriesHRM3.Points.AddXY(t.Item1, t.Item2);
                         }
                     }
 

As you see each Series is filled with die actual Date(x axis) and an double value (y axis).
My Problem is that in Chartarea 1 all Dates are displayd correctly, but in the other areas as OLE automation. Anyone know why?
Thanks.

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