Comment 14 for bug 1441460

I just stumbled over this issue, because I am experiencing similar behaviour on a freshly installed Xubuntu 17.04 Zesty Zapus:

In a logged in session my laptop cannot suspend and after some inactivity time it displays an "Access Denied" notification. The only constraint for me is, this issue occurs only when battery powered. Though, with the power cord plugged in, suspend after inactiity works, indeed.