I have a few Forerunner 305s. I bought my first many years ago which I love, so I have bought a few more when I find them on eBay to be sure I have at least one which works.
I think I was able to use Garmin Express in December but not any longer. I now get the "sorry,...." message. Same on two other forerunner 305s.
I followed a thread suggestion from 2015 and downloaded garmin express again, this time on a new computer but when I tried to use it this time I got this:
I am running Sierra on my Macs, but I was running it when garmin express worked too. I don't understand why it no longer works. What does Garmin map updater have to do with this?