ERROR:dbus.proxies:Introspect error on :1.303:/org/freedesktop/PackageKit: dbus.exceptions.DBusException: org.freedesktop.DBus.Error.NoReply: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken

Open file /etc/dbus-1/system.d/org.freedesktop.PackageKit.conf
Find the line
<allow send_interface=org.freedesktop.PackageKit"/>
Add following line after above line
<allow send_interface="org.freedesktop.PackageKit.Transaction"/>

Open file /etc/dbus-1/system.conf
Find both lines
<allow send_requested_reply="true" send_type="method_return"/>
<allow send_requested_reply="true" send_type="error"/>
and replace top line with following line
<allow send_requested_reply="true"/>
Now delete the bottom line.