I have the issue as well. I remedied it by setting the command in properties to:
gksudo synaptic -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/827878 Title: Synaptic can no longer be started from the menu: cannot run "synaptic- pkexec" To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/synaptic/+bug/827878/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs