There are a few solutions floating around the forums for the dreaded "There was an error installing an update" message. I've tried them all with my Nuvi 1370T, but neither worked. I had just purchased a lifetime US & Europe update subscription for $115 and the newest version of Garmin Express (4.3 something) would not let me install the updates. It ultimately came down to the fact that there was not enough space on my Nuvi to accept the entire update, but that was completely unclear based on the error message Garmin Express was showing.
- I finally found a solution by downloading an old Garmin Express version 3.2.27 here ->
- This version told me that my model of Nuvi is not supported by Garmin Express, and it told me to download the old Garmin Map Updater here ->
- When I went to update my device with the Map Updated, it clearly informed me that my device does not have enough space and I can either purchase an SD card, or use an alternate solution which was to select the region I wanted to update. I selected the countries that I needed and voila, it already downloaded & prepared the map update, and is halfway through installing the update.
What a headache this is. The newer the Garmin Express versions get the less informative they are. I've cycled through a few old versions and the older ones are more intuitive in informing you of the issue you're running into.
I hope this helps those having the same problem that I was facing.