Aggregate Function in GridView Inside Radpane

[Ubuntu]

Dear All,

I have integrate the aggregates functions in my gridview and it was working fine, before I just added the grid into a radpane.
This radpane is created using RegionAdapter to use Prism 4 regions inside radpanegroup.

It works fine for sometime and suddenly throws an exception, I sometimes undock/dock the radpane.

here is the complete error:

Message: Unhandled Error in Silverlight Application
Code: 4004
Category: ManagedRuntimeError
Message: System.NullReferenceException: Object reference not set to an instance of an object.
   at Telerik.Windows.Controls.GridView.AggregatesToGroupFooterAggregatesConverter.<>c__DisplayClass4.<Convert>b__1(AggregateResult f)
   at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
   at MS.Internal.EnumerableCollectionView.LoadSnapshotCore(IEnumerable source)
   at MS.Internal.EnumerableCollectionView.LoadSnapshot(IEnumerable source)
   at MS.Internal.EnumerableCollectionView.RefreshOverride()
   at System.Windows.Data.CollectionView.Refresh()
   at Telerik.Windows.Controls.GridView.GridViewFooterCell.AggregateResults_CollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
   at System.Collections.Specialized.NotifyCollectionChangedEventHandler.Invoke(Object sender, NotifyCollectionChangedEventArgs e)
   at System.Collections.ObjectModel.ObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at Telerik.Windows.Data.RadObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at Telerik.Windows.Data.RadObservableCollection`1.ResumeNotifications()
   at Telerik.Windows.Controls.GridView.GridViewDataControl.CreateAggregateResults()
   at Telerik.Windows.Controls.GridView.GridViewDataControl.CalculateAggregates()
   at Telerik.Windows.Controls.GridView.GridViewDataControl.OnItemsCollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
   at System.Collections.Specialized.NotifyCollectionChangedEventHandler.Invoke(Object sender, NotifyCollectionChangedEventArgs e)
   at Telerik.Windows.Data.DataItemCollection.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at Telerik.Windows.Data.DataItemCollection.OnCollectionViewCollectionChanged(NotifyCollectionChangedEventArgs e)
   at Telerik.Windows.Data.DataItemCollection.Telerik.Windows.Data.IWeakEventListener<System.Collections.Specialized.NotifyCollectionChangedEventArgs>.ReceiveWeakEvent(Object sender, NotifyCollectionChangedEventArgs e)
   at Telerik.Windows.Data.WeakEvent.WeakListener`1.Handler(Object sender, TArgs args)
   at Telerik.Windows.Data.QueryableCollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
   at Telerik.Windows.Data.QueryableCollectionView.RefreshOverride()
   at Telerik.Windows.Data.QueryableCollectionView.RefreshInternal()
   at Telerik.Windows.Data.QueryableCollectionView.RefreshOrDefer()
   at Telerik.Windows.Data.QueryableCollectionView.ProcessSynchronousCollectionChanged(NotifyCollectionChangedEventArgs args)
   at Telerik.Windows.Data.QueryableCollectionView.ProcessCollectionChanged(NotifyCollectionChangedEventArgs args)
   at Telerik.Windows.Data.QueryableCollectionView.OnSourceCollectionChanged(Object sender, NotifyCollectionChangedEventArgs args)
   at Telerik.Windows.Data.QueryableCollectionView.Telerik.Windows.Data.IWeakEventListener<System.Collections.Specialized.NotifyCollectionChangedEventArgs>.ReceiveWeakEvent(Object sender, NotifyCollectionChangedEventArgs args)
   at Telerik.Windows.Data.WeakEvent.WeakListener`1.Handler(Object sender, TArgs args)
   at System.Collections.ObjectModel.ObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at Telerik.Windows.Data.RadObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at Telerik.Windows.Data.ObservableItemCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at Telerik.Windows.Controls.DomainServices.DomainServiceCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at Telerik.Windows.Data.RadObservableCollection`1.ResumeNotifications()
   at Telerik.Windows.Controls.DomainServices.DomainServiceCollection`1.OnLoadOperationCompleted(LoadOperation`1 loadOperation)
   at System.ServiceModel.DomainServices.Client.DomainContext.<>c__DisplayClass13`1.<Load>b__11(LoadOperation lo)
   at System.ServiceModel.DomainServices.Client.LoadOperation.<>c__DisplayClass4`1.<Create>b__0(LoadOperation`1 arg)
   at System.ServiceModel.DomainServices.Client.LoadOperation`1.InvokeCompleteAction()
   at System.ServiceModel.DomainServices.Client.OperationBase.Complete(Object result)
   at System.ServiceModel.DomainServices.Client.LoadOperation.Complete(DomainClientResult result)
   at System.ServiceModel.DomainServices.Client.DomainContext.CompleteLoad(IAsyncResult asyncResult)
   at System.ServiceModel.DomainServices.Client.DomainContext.<>c__DisplayClass1b.<Load>b__17(Object )

Line: 54
Char: 13
Code: 0

and this how I defined the XAML for the aggregate function:

<telerik:GridViewDataColumn Header="Total Credit" DataMemberBinding="{Binding total_credit}" DataFormatString="{}{0:n}" IsReadOnly="{Binding IsEnabled}">
    <telerik:GridViewDataColumn.AggregateFunctions>
        <telerik:SumFunction Caption="" ResultFormatString="{}{0:n}"/>
    </telerik:GridViewDataColumn.AggregateFunctions>
</telerik:GridViewDataColumn>

Any help on this !!