Created Unassigned: how to use CheckComboBox with mvvm [20766]

hi
I am using the CheckComboBox ver 2.0.0 in my wpf mvvm project
but I seem unable to bind the selecteditems. when Bind selecteditems to a property in wpf exception errror
SelectedItems="{Binding SelectedItemAccountUnitGroup }
error:
'SelectedItems' property is read-only and cannot be set from markup. Line

how to save All checked items CheckComboBox to database?

i am using EF code First And Mvvm


but only one checked item CheckComboBox save to database

__this is my code__
__binding in wpf window:__
<xceedtoolkit:CheckComboBox Grid.Row="2" Grid.Column="3" Name="xccedcheck"
ItemsSource="{Binding AccountUnitGroupList }"
DisplayMemberPath="AccUnitGroupName"
ValueMemberPath="AccUnitGroupID"
SelectedValue="{Binding AccountUnitData.AccUnitGroupID}"
SelectedMemberPath="{Binding SelectedItemAccountUnitGroup, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"

IsDropDownOpen="false"
MaxDropDownHeight="100">

i am using SelectedValue="{Binding AccountUnitData.AccUnitGroupID}" to save to database but this metod only one checked item save

===========================================
viewmodel:

public AccountUnit AccountUnitData { get; set; } //this field for new Instance of my model in view model

public ObservableCollection<AccountUnitGroup> AccountUnitGroupList { get; set; }//this list load mylist to CheckComboBox

private AccountUnitGroup _selectedItemAccountUnitGroup;

public AccountUnitGroup SelectedItemAccountUnitGroup // this field for binding to SelectedItem or SelectedItems
{
get { return _selectedItemAccountUnitGroup; }
set
{
if (_selectedItemAccountUnitGroup != value)
{
_selectedItemAccountUnitGroup = value;

NotifyPropertyChanged("SelectedItemAccountUnitGroup");
}
}
}


please help me by sample with mvvm

thanks