LocalServer.InitializeAsync(() =>
{
    if (LocalServer.LicenseStatus != LicenseStatus.Valid)
    {
        MessageBox.Show("This ArcGIS Runtime license is not valid");
    }
    LocalGeoprocessingService lgs = new LocalGeoprocessingService(@"C:\...\GeoprocessingTool.GPK", GPServiceType.SubmitJob);
    lgs.StartAsync((d) =>
    {
        if (d.Error != null)
        {
            MessageBox.Show(string.Format("{0}", d.Error.Message));
        }
    });
});