After start of geprocessing service, I was facing this type of error.
The example of code is taken from Local server geoprocessing | ArcGIS for Developers
in .xaml.cs file
// Create a map image layer to show the results
ArcGISMapImageLayer myMapImageLayer = new ArcGISMapImageLayer(new Uri(gpServiceResultUrl));
// Load the layer
await myMapImageLayer.LoadAsync();
at await myMapImageLayer.LoadAsync(); it was getting load error "unknown operation:Get Mapserver/jobs/j89....
please resolve the issue
Michael Branscomb