Your device is in MTP mode (Media Transfer Protocol) so it's .System folder isn't visible (see below*). There are most likely unlocked detail maps in that folder which are causing the problem.

WebUpdater does not reside on the device itself. It's a computer program, get it from here:
Code:
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If you don't wish to use WebUpdater and prefer to simply load the GCD file manually, download the V5.60 file and change file name "nuvi55_56_560.gcd" to "gupdate.gcd". *Make .System folder visible on your PC, read [Only registered and activated users can see links. ]. To set your device to Mass Storage Mode (MSM), see [Only registered and activated users can see links. ]. Then connect to PC so you can place gupdate.gcd in the .System folder.

If you haven't patched the firmware you cannot use unlocked Unicode maps (codepage 65001, such as Europe NTU). You can however use NT maps (CP 1252) which are unlocked with latest gimgunlock. Units such as nuvi 53/55/56/65/66 contain a 'weak' MSV check. So those devices only need patching for Unicode map use, or alternatively you can do [Only registered and activated users can see links. ] to use Unicode mapping.