Back again. RMPrepUSB loaded up and 550 now correctly formatted ok showing 1.93GB on the hard disk. But the Unbrick a Nuvi shows GarminCure3 v0.1 to flash original instead of cure firmware into the unit. I had only used GarminQuickCure which was different to that shown on the Unbrick pages?
Where do we go from here?

(EDIT 1) Great stuff Butters indebted to you. The Zumo 550 now loads up all the European maps ok and runs as before having updated everything on the Garmin Express site. One little change is that it always showed a bike or car icon and now when I set it up all I get is an arrow on the map? Went in to change the settings to bike but arrow keeps appearing all the time?
New Garmin can wait a year or two now.

(EDIT 2) Hi Butters.

Indebted to you. Zumo 550 now talks to Garmin Express and loaded up all the maps again with a 4GB SD card. All seems to be functioning again apart from the icon on the screen? All I get now is the arrow icon and not my choice of car or bike? Went to settings and touched the bike icon but the map still stays on the arrow? Any ideas on this one Butters. Otherwise one very happy bunny.
Friendly reminder to not make consecutive posts, please edit your previous post if you need to add or correct info to it. Required in our [Only registered and activated users can see links. ] here. I've combined the 3 posts and done it like 'edits' for you this time.

PS: Welcome to GPS Power. Glad you've been helps here.