WPF Disptacher processing error - wpf

Question

I have the following xaml in my WPF project
<ItemsControl ItemsSource="{Binding ParentJob.JobSamples}" Grid.Row="3" Grid.Column="0" Grid.ColumnSpan="2">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Expander ExpandDirection="Down" IsExpanded="{Binding Path=IsExpanded}">
<Expander.Header>
<BulletDecorator>
<Label Content="{Binding Identifier}"></Label>
</BulletDecorator>
</Expander.Header>
<ItemsControl ItemsSource="{Binding Path=SelectedAnalyticalTests}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Vertical"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<CheckBox Margin="4" Content="{Binding AnalyticalTestName}" Foreground="{DynamicResource InputFontColor}" Checked="{Binding IsSelected}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</Expander>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
My objects are set up such that ParentJob has an ObservableCollection of JobSample objects
and JobSample has an ObservableCollection of AnalyticalTest objects called SelectedAnalyticalTests
If I load up a ParentJob that has JobSamples that don't contain any SelectedAnalyticalTests I get each of the JobSamples listed correctly.
If I attempt to load a ParentJob that has JobSamples that do have SelectedAnalyticalTests I get the following error:-
'Disptacher processing has been suspended, but messages are still being processed'
Has this got to do with my IsExpanded attribute? How can I get around this?
The ViewModel is broken up into 3 partial classes as follows:-
public partial class JobRepeatViewModel : ViewModelBase
{
public JobRepeatViewModel(MainWindowViewModel mainWindowVM)
{
this.MainWindowViewModel = mainWindowVM;
try
{
DependencyObject dep = new DependencyObject();
if (DesignerProperties.GetIsInDesignMode(dep))
{
return;
}
this.DA = new ACSDataAccess();
LoadDropdowns();
}
catch (Exception ex)
{
MessageBox.Show(ex.InnerException.ToString());
}
}
private void LoadDropdowns()
{
this.StaffMembers = this.DA.GetStaffMembers();
}
}
public partial class JobRepeatViewModel : ViewModelBase
{
public void OnJobRepeatAnalysisSavePopUpClicked(object sender, RoutedEventArgs e)
{
if (this.OnSavePopUpClicked != null)
{
this.OnSavePopUpClicked(sender);
}
}
public void OnJobRepeatAnalysisCancelPopUpClicked(object sender, RoutedEventArgs e)
{
if (this.OnCancelPopUpClicked != null)
{
this.OnCancelPopUpClicked(sender);
}
}
public void Execute_SaveRepeatJobClick()
{
}
}
public partial class JobRepeatViewModel : ViewModelBase
{
public event JobRepeatAnalysisCancelPopupClicked_Event OnCancelPopUpClicked;
public delegate void JobRepeatAnalysisCancelPopupClicked_Event(object sender);
public event JobRepeatAnalysisSavePopupClicked_Event OnSavePopUpClicked;
public delegate void JobRepeatAnalysisSavePopupClicked_Event(object sender);
public MainWindowViewModel MainWindowViewModel
{
get { return Get(() => MainWindowViewModel); }
set { Set(() => MainWindowViewModel, value); }
}
public Job ParentJob
{
get { return Get(() => ParentJob); }
set { Set(() => ParentJob, value); }
}
public ACSDataAccess DA
{
get { return Get(() => DA); }
set { Set(() => DA, value); }
}
public ObservableCollection<Staff> StaffMembers
{
get { return Get(() => StaffMembers); }
set { Set(() => StaffMembers, value); }
}
}