I had that page last Thursday even though others were getting in.
That's when i tried connect.garmin.com without the /modern at the end and it's been fine ever since for me.
Perhaps, yours is a geographic issue. Does mobile work?
My garmon vivofit was working perfectly fine and then earlier this week I connected the my fitness app and as of yesterday it stopped tracking on the calendar. Hence the network error and as of this morning I noticed it's not tracking my sleep. Augh! I hope someone can help me, I removed the device from my iPhone and reconnected it, I took my fitness app off and put it back on. I really like this vivofit. I had issues with Fitbit and eventually gave up on it. I don't want to deal with issues again