Before you start replacing modules all over the place, it's best to zero in on the actual cause of the problem. I'd put money on it being a faulty nav drive (not the whole module, just the drive or maybe even just the laser unit).
Concentrate on the nav unit. You should be able to eject the disc by holding down the eject button. Sometimes this can take a minute or two. Hopefully it will come out and you can see if the network runs ok without a nav disc (effectively jumping out the nav drive from the loop). If not, disconnect the nav unit with a fibre optic ring either bought from a dealer or borrowed from a friends car... Don't use the one in your glovebox as you'll just be creating another break in the loop).
If the network functions ok, you've found the problematic module. This can probably be repaired.