Cannot connect to software update server
Check you're using the correct command - there were a few variants for different OS versions, but this will work for 10.10 onwards, including 10.12 Sierra:
sudo softwareupdate --clear-catalog
Check you're using the correct command - there were a few variants for different OS versions, but this will work for 10.10 onwards, including 10.12 Sierra:
sudo softwareupdate --clear-catalog