I am experiencing the same issue. I.e; "there was an error installing the update" I have tried everything including watch re-set (at the expense of losing my last few activities) so this is fast becoming frustrating. There is no indication as to WHAT the damned error is!
I am also on a Mac, so wondering if this is where the issue lies?? Can Garmin please assist me.
You'll need to contact Garmin Support from the support site as there are any number of reasons why. it could be as simple as a poor connection to the Garmin servers that might correct itself. It could be an issue on the watch. It could be a problem with Garmin Express.
I think it's unlikely to be an issue with the Mac as I've been using Macs with Garmin products for many years.
only the Forerunner that I have (310XT) doesn't even show up on their Support drop down list. Maybe for good reason who knows?? I've found a phone number so hopefully someone can assist
I think the only reason for it not appearing in the Garmin list is because of its age.