Getting System.InvalidOperationException: 'Collection was modified; enumeration operation may not execute.'

[prasannapad]

Get the following exception:
System.InvalidOperationException
HResult=0x80131509
Message=Collection was modified; enumeration operation may not execute.
Source=mscorlib
StackTrace:
at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
at System.Collections.Generic.List1.Enumerator.MoveNextRare() at System.Collections.Generic.List1.Enumerator.MoveNext()
at SensiEdgeDemo.Domain.AccGyroMagViewModel.b__23_0() in C:\Users\prp\Documents\SensiBleWindows-master\SensiEdgeDemo\Domain\AccGyroMagViewModel.cs:line 95
at System.Windows.Threading.DispatcherOperation.InvokeDelegateCore()
at System.Windows.Threading.DispatcherOperation.InvokeImpl()

here:

var z = new LineSeries() { Fill = Brushes.Transparent, Foreground = Brushes.Blue, PointGeometry = null, Values = new ChartValues() };
foreach (var kvp in Values)
{
switch (SelectedIndex)
{
case 0:
x.Values.Add(new ObservablePoint(kvp.Key, GetValue(kvp.Value.Acc.X)));
y.Values.Add(new ObservablePoint(kvp.Key, GetValue(kvp.Value.Acc.Y)));
z.Values.Add(new ObservablePoint(kvp.Key, GetValue(kvp.Value.Acc.Z)));
break;
case 1:
x.Values.Add(new ObservablePoint(kvp.Key, GetValue(kvp.Value.Gyro.X)));
y.Values.Add(new ObservablePoint(kvp.Key, GetValue(kvp.Value.Gyro.Y)));
z.Values.Add(new ObservablePoint(kvp.Key, GetValue(kvp.Value.Gyro.Z)));
break;
case 2:
x.Values.Add(new ObservablePoint(kvp.Key, GetValue(kvp.Value.Mag.X)));
y.Values.Add(new ObservablePoint(kvp.Key, GetValue(kvp.Value.Mag.Y)));
z.Values.Add(new ObservablePoint(kvp.Key, GetValue(kvp.Value.Mag.Z)));
break;
}
}

...\SensiEdgeDemo\Domain\AccGyroMagViewModel.cs