E: There are problems and -y was used without --force-yes

2015-11-03 02:39:55.761 | WARNING: The following packages cannot be authenticated!
2015-11-03 02:39:55.761 |   screen
2015-11-03 02:39:55.764 | E: There are problems and -y was used without --force-yes
2015-11-03 02:39:55.766 | + exit_trap
2015-11-03 02:39:55.766 | + local r=100
2015-11-03 02:39:55.767 | ++ jobs -p

Solution1:
# apt-get update

Solution2:
Add to /etc/apt/apt.conf:
APT::Get::AllowUnauthenticated 1 ;