Well, a screenshot should do the explaining really.
I recently installed a UI, which replaced my WTF folder as well as interface. The UI (as some of you may recognize) is FabUI that Ideal Max shared. After looking through the game files, I noticed that quite a lot of the files have been changed to be the author of the UIs characters etc. (Such as the TotalRP3.lua located in D:\RPHTinyLegion\WTF\Account\blank\SavedVariables) This also occurs in other files in the WTF folder, which I tried to replace with files from my second client containing different patches. Yet this problem still occurs.
Yes I do realize that the error message points me to the Interface folder, but it didn't look like much could be fixed there (I'm no good with these kinds of things so I may be wrong about this).
If any helpful souls could aid me in fixing this; first of all that would be amazing. Secondly and lastly if you need more information just let me know in the replies.