Combobox inside RadGridView

[Karthik]

I have a RadGridView inside which I have a GridViewComboBoxColumn. For some reason my combo box column always appears to be empty. All the other columns seems to bind with the ItemSource properly

Here is how my RadGridView looks like

<telerikGrid:RadGridView x:Name="VGrid" d:LayoutOverrides="Width" Grid.Row="1" Grid.ColumnSpan="2"
RowIndicatorVisibility="Collapsed" MinHeight="100" ShowGroupPanel="False"
 AutoGenerateColumns="False" ItemsSource="{Binding Rows}">

Row is a simple class which has a bunch of string properties and also a collection of objects called Source.
Source is also a simple class with properties, id and name.

My Combobox column looks like this

<telerikGrid:GridViewComboBoxColumn Header="Source" IsSortable="True"
ItemsSource="{Binding Sources}" DataMemberBinding="{Binding id}"
SelectedValueMemberPath="{Binding id}"  ></telerikGrid:GridViewComboBoxColumn>

I have read a lot of posts similar to the problem that am facing, but couldn't really figure out why my combo box column is empty.
(Of course I have checked more than once that my Sources collection in Row is not empty).

Any ideas, clues will be greatly appreciated

Thanks
K