I have now spent a lot of time looking at the Nurb Surfaces issue with AutoCAD 2015/2016/2017, and it looks like a serious bug in the AutoCAD API. I have posted this on the AutoCAD API forum (http://forums.autodesk.com/t5/net/error-in-subdmesh-getobjectmesh/td-p/6275092) - so will hopefully get a response which will result in a resolution of this problem. Until then, I suggest users stay with AutoCAD 2014.
Paul