I also cannot create manual entries in Activities. As of right now on http://connect.garmin.com/en-US/status it says activities are fixed but there are obviously still issues.
Same problem however, if you switch to classic view mode, you can add manually. Also, if you want to upload manually and pick certain activities you can only do this on classic mode. Wait, you have the option to do this ONLY on classic mode but that doesn't work either.
