Two way datatable binding in WPF - wpf

Question

I have a datagrid (A C1 datagrid, in this case) bound to a property in my View Model. The XAML for the datagrid looks like this:
<c1:C1DataGrid
AutoGenerateColumns="False"
IsReadOnly="False"
Margin="5" Width="auto"
MinWidth="250"
HorizontalAlignment="Stretch"
VerticalAlignment="Stretch"
Name="dgNotifAssign"
CanUserAddRows="True"
ItemsSource="{Binding Path=notifCodeSubs.notification_configuration}"
>
<c1:C1DataGrid.Columns>
<c1:DataGridTextColumn
Binding="{Binding Path=user_id}"
Header="Recipient"
VerticalAlignment="Stretch"
SortMemberPath="user_id"
>
The property that it is bound to, in my viewmodel, looks like this:
Public Property notifCodeSubs As dsPeruseFM
Get
If _notifCode Is Nothing Then
_notifCode = New dsPeruseFM
End If
Return _notifCode
End Get
Set(ByVal value As dsPeruseFM)
MsgBox("If you can see this, success!")
End Set
End Property
In the codebehind I create an instance of the viewmodel and set the datacontext of the xaml to that instance, rather simple...
Dim vm As New ctrlAlertNotifyVM
As well as:
ctrlAlertNotifyXML.DataContext = vm
The above configuration compiles and reads data just fine. The grid is populated with all the correct data, etc. The problem comes when I try to add Mode=twoway to the ItemsSource on the datagrid. At that point VS2010 spits out the following error:
A TwoWay or OneWayToSource binding cannot work on the read-only property 'notification_configuration' of type 'PeruseFM.dsPeruseFM'.
I'm quite sure that all of my properties are read/write. And while the set command for this is nothing more than a message box at this point, it doesn't seem like I can even access that.
So the question is... has anybody ever encountered this issue before?
Update, response to question "What does notification_configuration look like?" from sixlettervariables:
Public Function codeChanged(Optional ByVal x As String = "")
If _notifCode Is Nothing Then
_notifCode = New dsPeruseFM
End If
taNotifSubs.fillNotifSubs(notifCode:=x, dataTable:=_notifCode.notification_configuration)
Return _notifCode
End Function

Answer 1

You've shown us that notifCodeSubs is read/write, however, that is not the actual property you've bound to.
From this viewpoint, the error message is fairly self-explanatory:
...read-only property 'notification_configuration'...
Therefore you cannot apply TwoWay binding to that property as an ItemsSource.