Thanks for the reply Hugo.I am loading the feature using this code is it going to work.
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void queryTask_ExecuteCompleted(object sender, ESRI.ArcGIS.Client.Tasks.QueryEventArgs e)
        {
            GraphicsLayer graphicsLayer = Map.Layers["MyGraphicsLayer"] as GraphicsLayer;
            graphicsLayer.ClearGraphics();
            FeatureSet featureSet = e.FeatureSet;
            
            if (featureSet != null && featureSet.Features.Count > 0)
            {   
                foreach (Graphic resultFeature in featureSet.Features)
                {                    
                    graphicsLayer.Graphics.Add(resultFeature);
                }
                System.Windows.Data.Binding bind = new System.Windows.Data.Binding();
                bind.ElementName = "Map";
                bind.Path = new PropertyPath("Layers.[MyGraphicsLayer]");                
                MyDataGrid.SetBinding(ESRI.ArcGIS.Client.Toolkit.FeatureDataGrid.GraphicsLayerProperty, bind);
                MyDataGrid.UpdateLayout();       
            }
            else
            {
                MessageBox.Show("No features Returned from Query", "Query", MessageBoxButton.OK);
                MyDataGrid.Columns.Clear();
                foreach (KeyValuePair<string, string> kv in featureSet.FieldAliases)
                {
                    DataGridTextColumn dt = new DataGridTextColumn();
                    Binding b = new Binding("Attributes");
                    b.Converter = new ESRI.ArcGIS.Client.ValueConverters.DictionaryConverter();
                    b.ConverterParameter = kv.Key;
                    dt.Binding = b;
                    dt.Header = kv.Value;                    
                }      
            }
            
        }
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After adding your code the silverlight control just disappeared and whole screen becomes blank.I am 
using following code
[HTML]
<esri:FeatureDataGrid VerticalAlignment="Bottom" IsReadOnly="True" HorizontalAlignment="Stretch" x:Name="MyDataGrid"  Height="162" Margin="0,0,1,2" GraphicsLayer="{Binding ElementName=Map, Path=Layers.[Sewer_Lines]}" BorderBrush="Black" BorderThickness="1" Grid.RowSpan="2" SelectionChanged="MyDataGrid_SelectionChanged" MouseLeftButtonDown="MyDataGrid_MouseLeftButtonDown"></esri:FeatureDataGrid>
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