From ESRI Silverlight API Help, it is recommended to use Synchronous geoprocessing services rather than the Asynchronous ones. If the published geoprocessing service is in the Execution Type: esriExecutionTypeAsynchronous, can it be executed as a synchronous one? Conversely, If the published geoprocessing service is in the Execution Type: esriExecutionTypeSynchronous , can it be executed as an asynchronous one? Thanks for your review and feedback.