Question Cannot build/use signs when someone is OP

Hi, I have been trying to solve a problem on my server for hours upon hours but simply cannot find a solution. When no player on the server is set to OP (/op {player}) all players can brake, place and most importantly, click join signs to join mini games. However as soon as I make ANY player on the server OP all other players on the server that are not OP can no longer place/destroy blocks or click the signs to join minigames. I have listed the plugins I am using and my config files below although I have already tried disabling worldguard, essentials protect, ultimatehub and groupmanager (so I don't know if it is a problem with permissions or not?) I will also add that the join signs players cannot use do not require any permission nodes to do so.

Spigot Version: 1.8.1
Plugins Installed:

Essentials Config: http://pastebin.com/NNW24k11
Groups.yml: http://pastebin.com/8PtcHNN3

Any help would be greatly appreciated as I've no more ideas on how I can fix this. If you require any more info please let me know. Many Thanks!