the featurelayer works well when the data is in file geodatabase,but i change the datasource to the data in sde for sqlexpress ,the featurelayer can't be seen,and there is no error occured in application.
We need to know if your issue is coming from the Silverlight API or from ArcGIS Server.
Using 'ARcGIS Service Manager', do you see your service as started? Using 'ArcGIS Services Directory', can you browse to your service and display it (using ArcGIS Javascript for example) ?
