Complex terrain model "Object Reference not set to an instance of an object"

I have a complex terrain model that is comprised from terrain models in two reference files.  The primary is an overall base mapping terrain model, and the other reference dgn contains several smaller terrain models that we are merging in to the complex.  The problem is that the complex terrain model allready has 30+ terrain models merged.  I need to add more, but when I go to Edit Complex Terrain Model, I get the "Object reference not set to an instance of an object." error, and none of the TMs already merged show as being in the Complex TM.  See screenshots below.  When I select the complex model and in Element Properties select Edit it gives me the "Object reference" error, as shown in the 1st screenshot below.  If I hit OK, it doesn't show any terrain models in the Edit dialog.  If i close the dialog, deselect the terrain model, and select Edit Complex Terrain Model from the task bar, it opens the Edit dialog and shows all the terrain models available, but it doesn't show any of the terrains already merged in (Screenshot 2).  You can see in the first screenshot in the Element Properties window all the TMs aready in the Complex TM.  I don't want to go back and rebuild the complex model for fear of loosing any previous information.

I am working in a ProjectWise environment and all the files are in ProjectWise.

PowerInRoads V8i (SS4) V