You don't give the properties for your UserGroup class, but if you want to bind the SelectedItem you need to identify a property in the UserGroup class that is unique to each UserGroup and then you need to bind the SelectedValue property and the SelectedValuePath to this property. So, just say your UserGroup class had a property called UserGroupID then you would set the SelectedValue property like this
<DataTemplate>
<ComboBox
SelectedItem="{Binding Path=UserGroup, Mode=TwoWay}"
SelectedValue="{Binding SelectedDocTypeAcces.UserGroup.UserGroupID}"
SelectedValuePath="UserGroupID"
ItemsSource="{Binding Path=DataContext.UserGroupList,
RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}"
IsReadOnly="False" Background="White" />
</DataTemplate>
I hope this makes sense. If not please post your UserGroup class code and We can work from there.
[Edit] By the way, this assumes you have a property in your ViewModel that returns an instance of a DocAccessType class called
SelectedDocAccessType
, which is bound to your DataGrid's
SelectedItem
property.[/Edit]