Combobox binding Problem i am using wpf and entity framework

<Window.Resources>
        <CollectionViewSource x:Key="Centerlist" />
        <CollectionViewSource x:Key="Centerlist1"/>
        <CollectionViewSource x:Key="ItemList"/>
<CollectionViewSource x:Key="MasterViewSource" />
        <CollectionViewSource Source="{Binding TransferDetails, Source={StaticResource MasterViewSource}}" x:Key="DetailsViewSource" />
</Window.Resources>
    <Grid Background="{DynamicResource InputBackgroundBrush}" DataContext="{Binding Source={StaticResource MasterViewSource}}">
    <Grid.RowDefinitions>
    <RowDefinition Height="0.112*"/>
    <RowDefinition Height="0.08*"/>
    <RowDefinition Height="0.073*"/>
    <RowDefinition Height="0.091*"/>
    <RowDefinition Height="0.551*"/>
    <RowDefinition Height="0.093*"/>
    </Grid.RowDefinitions>
    <StackPanel Grid.Row="1" Orientation="Horizontal" HorizontalAlignment="Right">
    <TextBlock TextWrapping="Wrap" Text="Date:" HorizontalAlignment="Center" VerticalAlignment="Center" Style="{DynamicResource AvatarTextBlockStyle}"/>
            <telerik:RadDatePicker x:Name="Transferdate" VerticalAlignment="Center" HorizontalAlignment="Center" Width="93.157" SelectedValue="{Binding TransferDate}"/>
    </StackPanel>
    <StackPanel Grid.Row="2" Orientation="Horizontal">
    <TextBlock TextWrapping="Wrap" Text="SourceCenter:" VerticalAlignment="Center" Style="{DynamicResource AvatarTextBlockStyle}" Margin="5,0,0,0"/>
    <telerik:RadComboBox x:Name="cmbSourcecenter"
                                 ItemsSource="{Binding Source={StaticResource Centerlist }}"
                                 DisplayMemberPath="CenterName"
                                 OpenDropDownOnFocus="True"
                                 IsEditable="True"
                                 SelectedItem="{Binding CenterMaster}"
                                 Width="140" HorizontalAlignment="Center" 
                                 VerticalAlignment="Center" 
                                 Style="{DynamicResource Customradcombobox}" 
                                 Height="25" 
                                 DropDownOpened="cmbSourcecenter_DropDownOpened" >
    </telerik:RadComboBox>
    <TextBlock TextWrapping="Wrap" Text="To" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="15,0" Foreground="#FFDA1A1A" FontSize="13.333"/>
    <TextBlock TextWrapping="Wrap" Text="DestinationCenter:" HorizontalAlignment="Center" VerticalAlignment="Center" Style="{DynamicResource AvatarTextBlockStyle}"/>
    <telerik:RadComboBox x:Name="cmbdestinationcenter"
                                 Width="140" 
                                 ItemsSource="{Binding Source={StaticResource Centerlist1}}"
                                 DisplayMemberPath="CenterName"
                                 IsEditable="True"
                                 SelectedItem="{Binding CenterMaster}"
                                 OpenDropDownOnFocus="True"
                                 HorizontalAlignment="Center" 
                                 VerticalAlignment="Center" 
                                 Height="25"
                                 Style="{DynamicResource Customradcombobox}" 
                                 DropDownOpened="cmbdestinationcenter_DropDownOpened">
               
            </telerik:RadComboBox>
    </StackPanel>
    <StackPanel Grid.Row="3" Orientation="Horizontal">
    <TextBlock TextWrapping="Wrap" Text="Remark:" VerticalAlignment="Center" Style="{DynamicResource AvatarTextBlockStyle}"/>
    <telerik:RadWatermarkTextBox 
    x:Name="txtremark" 
    Text="{Binding Remark}"
    WatermarkContent="Remark" TabIndex="2" VerticalAlignment="Center" Width="270.45" />
    </StackPanel>
        <StackPanel Grid.Row="4">
        <DataGrid AutoGenerateColumns="False"  
        HorizontalAlignment="Stretch" 
        x:Name="CenterGrid"
        IsSynchronizedWithCurrentItem="True"
        CanUserAddRows="True"
        CanUserDeleteRows="True" 
                    
        Focusable="True"
                 
        ItemsSource="{Binding Source={StaticResource DetailsViewSource}}" 
        TabIndex="4"  SelectionMode="Single" FontSize="10.667" HeadersVisibility="Column" >

        <DataGrid.Columns>

        <DataGridComboBoxColumn x:Name="cmbCentername" Header="ItemName"
        ItemsSource="{Binding Source={StaticResource ItemList}}"
        SelectedItemBinding="{Binding ItemMaster}"
        DisplayMemberPath="ItemName"
        SelectedValuePath="ItemId"
        Width="150" HeaderStyle="{DynamicResource DataGridColumnHeaderStyle1}">
        <DataGridComboBoxColumn.EditingElementStyle>
        <Style TargetType="{x:Type ComboBox}">
        <Setter Property="IsEditable" Value="True" />
        <Setter Property="IsDropDownOpen" Value="True"/>
        </Style>
        </DataGridComboBoxColumn.EditingElementStyle>
        </DataGridComboBoxColumn>

        <DataGridTextColumn  x:Name="txtqty" Header="Qty" Width="*" Binding="{Binding Qty, UpdateSourceTrigger=PropertyChanged}" HeaderStyle="{DynamicResource DataGridColumnHeaderStyle1}"  />
        </DataGrid.Columns>
        </DataGrid>
        </StackPanel>
        <StackPanel Grid.Row="5" Orientation="Horizontal">
        <Button x:Name="btnNew" Content="New" Height="29" Width="70" RenderTransformOrigin="0.493,-0.349" Click="btnNew_Click" Style="{DynamicResource imagebutton}" Margin="0,0.978,5,14.01" HorizontalAlignment="Right"/>
        <Button x:Name="btnview" Height="29" Width="70" Click="btnview_Click" Style="{DynamicResource NormalButtonStyle}" Content="View" Margin="0,0.978,5,14.01" HorizontalAlignment="Right" />
        <Button x:Name="btnSave" Content="Save" Height="29" Width="70" Click="btnSave_Click" RenderTransformOrigin="0.5,0.5" Style="{DynamicResource NormalButtonStyle}" Margin="0,0.978,5,14.01" TabIndex="14" HorizontalAlignment="Right" />
        <Button x:Name="btnDelete" Content="Delete" Height="29" Width="70" Click="btnDelete_Click" Style="{DynamicResource NormalButtonStyle}" BorderThickness="3,3,475,3" Margin="0,0.978,0,14.01" HorizontalAlignment="Right"/>
        </StackPanel>

    </Grid>

code Behind
------------------------------------------------
namespace HTBookSystem.Form
{
    /// <summary>
    /// Interaction logic for TransferDetail.xaml
    /// </summary>
    public partial class TransferData : Window
    {
        HTBookEntities book = new HTBookEntities();
        IList<Transfer> Transferdata;
        IList<TransferDetail> Transferdatalist;
        private CollectionViewSource MasterViewSource;
        private CollectionViewSource DetailViewSource;
        Transfer Tra;

        int iid;
        DataGridForm dgf;

        public TransferData()
        {
            InitializeComponent();
        }

        private void btnNew_Click(object sender, RoutedEventArgs e)
        {
            iid = 0;
            MethodMasterView();

        }

        private void btnview_Click(object sender, RoutedEventArgs e)
        {
            Tra = new Transfer();
            dgf = new DataGridForm();
            var grid = Tra.GridTransfer();
            dgf.GridFormText("Outward");
            iid = dgf.Returnid(grid);
            MethodMasterView();
        }

        private void btnSave_Click(object sender, RoutedEventArgs e)
        {
            foreach (var idetail in Transferdatalist)
            {
                if (idetail.Transfer == null)
                {
                    book.DeleteObject(idetail);
                }
            }

        try
        {
            book.SaveChanges();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }
        MessageBox.Show("Transfer data saved.", this.Title, MessageBoxButton.OK, MessageBoxImage.Information);
       
        }

        private void btnDelete_Click(object sender, RoutedEventArgs e)
        {
            if (MessageBox.Show("Are you Sure To Delete This Entry?", "Question", MessageBoxButton.YesNo, MessageBoxImage.Warning) == MessageBoxResult.No)
            {

            }
            else
            {
                book.DeleteObject(Tra);
                book.SaveChanges();
                MessageBox.Show("Entry  Successfully deleted");
            }
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            IQueryable<ItemMaster> itemlist = from i in book.ItemMasters select i;
            
            this.MasterViewSource = (CollectionViewSource)this.FindResource("MasterViewSource");
            this.DetailViewSource = (CollectionViewSource)this.FindResource("DetailsViewSource");
            CollectionViewSource productSource = (CollectionViewSource)this.FindResource("ItemList");
            productSource.Source = itemlist.ToList();
            var Centerlist = (from i in book.CenterMasters orderby i.CenterName select i);
            CollectionViewSource Namesource = (CollectionViewSource)this.FindResource("Centerlist");
            Namesource.Source = Centerlist.ToList();
            var Centerlist1 = (from i in book.CenterMasters orderby i.CenterName select i);
            CollectionViewSource Destinationsource = (CollectionViewSource)this.FindResource("Centerlist1");
            Destinationsource.Source = Centerlist1.ToList();
            this.MasterViewSource.Source = this.Transferdata;
            iid = 2;
            MethodMasterView();

        }


        public void MethodMasterView()
        {

            if (iid == 0)
            {
                 Tra= new Transfer();
                book.Transfers.AddObject(Tra);
            }
            else
            {

                Tra = (from i in book.Transfers.Include("TransferDetails")
                       where i.TransferId == iid
                       select i).First();


            }


            Transferdata = (from i in book.Transfers.Include("TransferDetails")
                           where i.TransferId == 0
                           select i).ToList();


            Transferdata.Clear();
            Transferdata.Add(Tra);

            
             
            Transferdatalist = Tra.TransferDetails.ToList();

            this.MasterViewSource.Source = this.Transferdata;
        }

        private void cmbSourcecenter_DropDownOpened(object sender, EventArgs e)
        {
            var Centerlist = (from i in book.CenterMasters orderby i.CenterName select i);
            CollectionViewSource Namesource = (CollectionViewSource)this.FindResource("Centerlist");
            Namesource.Source = Centerlist.ToList();
        
        }

        private void cmbdestinationcenter_DropDownOpened(object sender, EventArgs e)
        {
            var Centerlist1 = (from i in book.CenterMasters orderby i.CenterName select i);
            CollectionViewSource Namesource = (CollectionViewSource)this.FindResource("Centerlist1");
            Namesource.Source = Centerlist1.ToList();
          
        }
      

    }

---

Dipak Sutare