CSLA's ReadOnlyListBase and the List<T> I converted it to both had the same objects in it. I am wondering what criteria Infragistics components (like the grid here) look for to determine whether a data source is read only or not. Is there some standard interface or something?

Thanks for your reply Mike. It turns out the list I was using for the data source was derived from CSLA ReadOnlyListBase. Calling ToList() on the read one makes the drop down appear. The objects in the list are editable and the same that were there in the 'read only' version however. What constitutes a read only list to the UltraGrid?