ElementName Binding is failing

I'm guessing that the writer of Chart, when deriving from FrameworkElement or whatever, failed to realize that they needed to add any child elements to the logical tree either manually or through an override. You don't get that for free when deriving.

Breaking the logical tree breaks the ability of children to bind by ElementName.

If you are the author of the Chart object, you can see this related question and answer.

You might not have a namescope where you try to bind, you could try to replace the ElementName construct with Source={x:Reference DisplayMarkers}.

The gist of it is that if you have elements in XAML which are not in the visual or logical tree you will not be able to use certain bindings like RelativeSource and ElementName, I suspect that DataSeries is not in any tree either (it sure sounds like it's abstract).

For a workaround for potential cyclical dependency errors see: https://stackoverflow.com/a/6858917/546730

For other readers, another possible cause is using a UserControl instead of a custom control for what's in the role of vf:Chart, above. I wrote a split button (in the role of the chart) and changing it from a UserControl to a custom control got my ElementName binding working.