Deselect the map you are not using, better to remove the old files; if you have both in nuvi, it's obvious it cant work properly.
You must have only one CNA gmapprom.img along it own new gmapprom.unl and gmapprom.gma.
Old .gma and .unl, gmapprom related, will prevent your new map to be recognized.
Look at maps list in nuvi, under "Maps" if it sees the new map.

This can help [Only registered and activated users can see links. ]
read post n2 too