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Thanks to both of you.
bhg, tried that thanks but no joy.
Tuvok. That's a good site I've bookmarked it.
In the meantime when I got back home I contacted garmin help. They had no answer. They suggested I update the satnav with garmin express. I told them I had already done it this morning as I usually do. They said try it again, it couldn't hurt. So I did and what do you know, I stuck a 0 on the end and this time it worked!!
I have no idea if the update did it or not, indeed I don't know why it would but there you go. Fingers crossed it stays working.
Thanks again for your replies.