Hi,
To use our API within the ElementHost you'll need to add the line below in order that the System.Windows.Application.Current is set (the API expects a WPF application). Just adding this line is enough.
...
new System.Windows.Application();
...
Cheers
Mike
Please note: On July 1, 2016, ArcGIS Runtime SDK for WPF entered the retired phase of its product life cycle. There will be no further updates to the product or its documentation. We recommend you explore WPF solutions based on the ArcGIS Runtime SDK for .NET. See this blog post for information on transitioning to the ArcGIS Runtime SDK for .NET.