I'm getting the same error with your addon. Everything works fine as soon as I remove your addon.
Windwhistle, you're linking to a post made almost 2 years ago, that contains screenshots of an error from a totally different addon than autopromote.
The error the user at the time gave, in my opinion as a developer, didn't include any hint of error due to Autopromote for XGUI.
That being said, if you'd please provide a copy / paste of the error(s) you are getting from your console that you experience, it would help anyone that still may wish to help with this (now pretty old in Gmod terms) 2.5 year old addon possibly do so.