I had saved the official Garmin page for downloading 15.77, perhaps it can be useful to some of you.
To backdate to public software:
Copy both the gupdate.gsp and force.tmp files from this zip, and place this in the Primary\Garmin folder of your watch.
When you disconnect from the computer your watch will prompt you to install this version of software. Note that this will reset all settings.
N.B. I had to make two threads (pro and nonpro) because the forum deletes threads with more than 3 links
Greetings