I suppose it's CNEU.
The latest official is NTU 2015.30. Unofficial is .40. NT latest official .20
You can have problems if you installed NTU version or if you got an .img made with Mapsource.
New CNs must be sent to device by Mapinstall, Mapsource is discontinued and not good with new CNs.
If you have lifetime update instead, try to reload the map, may be you got a faulty tile.
Be sure to have a basemap in nuvi too.
These are some ideas, if you give more details we can better understand your issue

sent with my phone