I have some trouble understanding what’s going on, so I’ll approach this from the other side:
Make sure there is a directory ‘\garmin’ on the removable disk that is your GPS.
(1) Unpack the osm_routable_gmapsupp.zip file that you’ve downloaded from the website.
(2) Place the unpacked gmapsupp.img in the ‘\garmin’ directory on your GPS.
(I believe the nuvi allows you to rename the file to aything, so you could try cyprus.img if there is already a gmapsupp.img in the ‘\garmin’ directory.)
(3) Reboot the GPS device and select the ‘OSM world routable’ map.
Note: if the unpacked file in (2) is named gmapsupp (without .img) or the osm_routable_gmapsupp.zip file in (1) is shown without the .zip extension then your operating system (Windows) does not show known filename extensions. You should then copy the file to the GPS and also not see the .img behind the filename, otherwise you’ve accidentally renamed it to gmapsupp.img.img
Hope this helps…