There might be an issue with the newest Nuvi Garmin firmwares.
It seems that Garmin has changed the way POIs are categorized.
Some units may support a couple of sub folders in the directory tree but it is not recommended to go further than one sub folder.
I've finally blown a fuse with Garmin's endless changes in GPI and GDB. Obviously, when we write a POI file we have no way of knowing which of "some units" may read them. I'm no longer investing major engineering time decoding their formats and implementing them. Without a published specification and notification of changes, the cost of staring a a pile of numbers trying to figure out what they changed this time is just more than I'm willing to invest.
The fact that none of the other couple hundred programmers on this list hopped on this message while I was on vacation says that there isn't a large group of others willing to do it, either.
I'm about one temper tantrum away from removing support for MPS, GDB and GPI.