The bits of software each have worthwhile functions, but why it cannot all be built into wizard's in one application defeats me.
I reckon your download is corrupt or incomplete. Move it to a trash directory and repeat the download.
My Europe NT 2013.41.gmap is 3.99 GB and I suppose files of this size are a challenge .Out of interest, what size is your download ?
An update:
Rang up Garmin Support this lunchtime and explained my problem. She could not explain why the 2014.10 download on my computer was not recognised by basecamp, but she guessed that it had got corrupted during the download. She also could not explain why in 14hrs Map Updater still failed to download the update! It wasn't looking promising at this point. Her only suggestion was to re-run Garmin Map Updater. I was dubious, but i ran through it all again (that said, early on in the process, she said that she needed to reset something and could I therefore restart the download process).
She also said that I should select "download to device and computer", as that was Garmin Supports recommendation. Although she said that some do prefer to download only to their computer, and then use Map Installer to load from computer to the Nav IV.
Anway, after another 2 hour or so wait, the download was completed and it worked: maps on both my Nav IV and Basecamp.
A couple of points raised during our conversation:
a) garmin are aware that there is an issue for some, as Garmin Express will not readily download updates to both the GPS and the computer. Their recommendation is to use Map Updater (not the Lifetime Map Updater). The latest version of Map Updater is v 4.2.2
b) There is some sort of beta of a new version of Garmin Express that they are "releasing to approx 10% of users". This version will download to both the device and the computer.
c) Garmin also recommend that we use a wired connection, not a wi-fi connection, when downloading the map updates. This is because the files are so large and are susceptable to interruptions in the internet connection.
d) make sure you disable the "energy saving" settings on your laptop/computer, again so that the download is not interrupted.
e) Apparently, Garmin Support do not recommend Micro SD cards larger than 8Gb for the 660/Nav IV. I did point out that if you have music on the device, then it is unlikely that an 8GB card would be big enough, given that the latest update is over 3GB. (In fact, when in Map Updater, it actually said that the download was 5.3GB+. She said that that was correct, but that the card only needed around 3Gb of spare capacity as some files would be overwritten)
So, there you have it. many thanks for the advice offered during my 'crisis'. i am off to play with Basecamp now!!