There is an invalid Curtain Panel in the model. This is probably caused by two Grid Lines almost meeting at a border of the Curtain Wall or Sloped Glazing, but not exactly at a point. The Curtain Panel can't be displayed. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
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