Update on the crashing 3590. I cleared the nonvol as suggested and though the unit worked faultlessly on a one hour drive i decided to check the unit indoors. I turned the GPS off and sat and scrolled the main europe map. After about 10 minutes it started slowing right down on the map loads eventually crashing the unit.

Initial thoughts would be an issue with pulling the map off the SD Card. However I'm pretty certain the SD card is fine. I've checked it in a Card reader, reformatted, etc and it gives fast data transfers and shows no writing or reading issues. Also the fact the card will work from the outset without issue would indicate the card itself is probably OK but maybe it's a problem with the Garmin unit accessing the card through whatever interface it uses.

I will put the Europe map on the Garmin - it should just fit and try this but it's not a complete solution as I like to use the Michelin guides in basecamp and they only work if installed on the Nuvi (and when they are there in not enough room for the NTU Europe.

Neil mentioned removing all other maps which I'll try, I notice that I've got gmapbmap.img on the Nuvi but also have gmapdem.img on the SD card a 317.8 MB file dated 10.01.2012. Should that be there? is it a worldwide basemap if so what is gmapbmap which I see is also referred to as a DEM?

Thanks.