There are huge unknown factors here, which make it hard for me to give you the answers you want. You've edited Essentials (you're making a game), and you've "upgraded" it - odds are you've tried to patch up your game rather than transfer your changes into the latest version as recommended.
The answers I provide work for Essentials. Any problems are caused by what you've been doing to it. You've most likely missed some of the code changes I've made since v9, which your error message does suggest.