Hi,
Without seeing your code, it's difficult to know exactly what the issue is. But try checking the Map properties?
Note this forum is for the product 'ArcGIS Runtime SDK for WPF' which was retired on July 1st 2016. The forum for the current ArcGIS Runtime SDK for .NET is: ArcGIS Runtime SDK for .NET. We recommend you move to ArcGIS Runtime SDK for .NET as soon as practical. In fact, we just released a beta for the next major release - if your project is in early stages we recommend starting with the beta: ArcGIS Runtime SDK for .Net | ArcGIS for Developers
Cheers
Mike