There is a class named LineSeries in the Charting assembly and there is another LineSeries class in the Chart assembly. You get the ambiguity error because both of these classes are mapped to the telerik schema. So when you write telerik:LineSeries, the xaml parser does not know which class you mean.
There is more than one way to sort this out, but we recommend that you fully remove the old Charting assembly and do not use the old RadChart at all. The new ChartView (in the Chart.dll) is much faster, it is very easy to set up and is also very flexible. It also resolves many of the limitations that the old control had.
I hope that you will be able to completely remove the Charting.dll reference from your project, and this error will be eliminated.
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