The addon works fine otherwise, been using it in pair with cartographer to help me find quests

This is at the TBC version

Edit by Muehe: embed image

QuestieTBC is not in active development currently. That being said, if you want to fix it yourself, you can try to remove this part from the file mentioned in the error message (that code is not in the master branch anymore).

Closed due to wontfix status. Feel free to ask additional questions in this issue if you require help on fixing it yourself.