I just started getting this error but I don't know how it is possible. The description of the error indicates that I've got two features on my map that have the same key...yet, in my testing I'm only placing ONE polygon on the map.
What else can it be if only one feature is being put on a map?
BTW, this has been working fine up to now, so I can't get what is different, except that I've added the following code: (but I commented it out and still get the error.)
DetailLayer.FeatureSource.Open();
MapControl.CurrentExtent = DetailLayer.FeatureSource.GetBoundingBox();
DetailLayer.FeatureSource.Close();
Bob