I recently purchased 2 Nuvi 310 (one for myself and one for a relative) and registered both of them under separate accounts. Both registered fine with the Webupdater. The first Nuvi was fine with the POI Loader but when I connected the 2nd Nuvi, it couldn't find the device even though it's showing up in My Computer. When I connect the 1st Nuvi again, POI Loader finds and recognises it but it still won't recognise the 2nd one. I even tried installing POI Loader onto another laptop and connecting the 2nd Nuvi first, but it doesn't detect it, although it will detect the 1st one Nuvi.
I have a Garmin Nuvi 660. Web Updater connects without a problem and the Nuvi shows up as a drive, but POI Loader doesn't recognize it. I had to put my POI's on an SD card and then put in the Nuvi to install them.
I have a Garmin Nuvi 310 that worked fine with the POI Loader untill I updated to a new version of the POI Loader , then I had the same problem. After for reasons other than this problem I had to redo my PC (Reinstalling Windows) I installed the new version of POI Loader and now it is working fine. I think it might have something to do with the data being written to the windows registry.