System.NotSupportedException: Invalid for root objects - use Delete instead

Hi Friends,

I'm new to CSLA and I'm currently working on one of our project done using CSLA. I'm getting the following exception when trying to remove an item from the collection. I tried the Delete method but that is not affecting the collection. Can you please shed some light on how to address this issue?

System.NotSupportedException was caught

  Message=Invalid for root objects - use Delete instead

  Source=Csla

  StackTrace:

       at Csla.Core.BusinessBase.DeleteChild()

       at Csla.Core.BusinessBase.Csla.Core.IEditableBusinessObject.DeleteChild()

       at Csla.BusinessListBase`2.DeleteChild(C child)

       at Csla.BusinessListBase`2.RemoveItem(Int32 index)

       at System.Collections.ObjectModel.Collection`1.RemoveAt(Int32 index)

Thanks,

Hemant.