Input string was not in a correct format

Hi,

I am using OxyPlot.WIndowsUniversal 2014.1.546.0 in a win8.1 project. I am trying to create a chart witth a category axis, a linear axis and a line series. However in the drawing space of the chart I am getting the following error.

OxyPlot exception: Input string was not in a correct format.
Stack trace: 
An exception of tpy[e System.FormatException was thrown when updating the plot model.
at System.Number.ParseDouble(String value, NumberStyles options, NumberFormatInfo numfmt)
at System.String.System.IConvertible.ToDouble(IFormatProvider provider)
at System.Convert.ToDouble(Object value)
at OxyPlot.Axes.Axis.ToDouble(Object value)
at OxyPlot.ReflectionExtensions.AddRange(List'1 target, IEnumerable itemsSource, String dataFieldX, String dataFieldY)
at OxyPlot.Series.DataPointSeries.UpdateItemsSourcePoints()
at OxyPlot.Series.DataPointSeries.UpdateData()
at OxyPlot.PlotModel.OxyPlot.IPlotModel.Update(Boolean updateData)

My code is this:

var chartModel = new PlotModel();
CategoryAxis categAxis = new CategoryAxis(); categAxis.Position = AxisPosition.Bottom;
 categAxis.ItemsSource = chartvm.DateValues;
 categAxis.LabelField = "MN";
 chartModel.Axes.Add(categAxis);
 LinearAxis linAxis = new LinearAxis();
 linAxis.Position = AxisPosition.Left;
chartModel.Axes.Add(linAxis);
var series = new LineSeries 
{
 Color = OxyColor.FromArgb(255, 78, 154, 6),
 DataFieldX = "MN",
 DataFieldY = "Value",
 ItemsSource = chartvm.DateValues
 };
 chartModel.Series.Add(series);
plotView.Model = chartModel;
DateValues is an ObservableCollection of type DateValue and DateValue is defined below.
 public DateValue(DateTime dateTime, double value, string monthName, bool isFiller) {
 _Date = dateTime;
 _Value = value;
 _mn = monthName;
 _isFiller = isFiller;
 }
 private DateTime _Date;
 public DateTime Date
 {
 get { return _Date; }
 set { _Date = value; }
 }
 private double _Value;
 public double Value
 {
 get { return _Value; }
 set { _Value = value; }
 }
 private string _mn;
 public string MN
 {
 get { return _mn; }
 set { _mn = value; }
 }
 private bool _isFiller;
 public bool IsFiller
 {
 get { return _isFiller; }
 set { _isFiller = value; }
 }

I can't understand why i'm getting the error. I have verified that the data is correct since it is displayed in a list next to the chart.

Thanks in advance for any help. It will be really appreciated.