You're absolutely right, Chris - problem solved.
In hindsight, I should have double-checked whether my colleague had followed the instructions in both steps after he reinstalled 2.2.1.
Thanks again for your help and have a good weekend.
The file health check was fine after we re-installed 2.2.1.
Unfortunately the error in my first post persists when trying to post a simple word ('test') in existing topics that we were able to post in before the 2.2.1 update.
Is anyone else getting the error on the screenshot below when trying to post a new thread/reply in Xenforo 2.1.1?
It's a Vanilla installation with 1 add-on installed (Amazon S3 add-on).
Note: I am unable to replicate the error in a test thread here at the official Xenforo forum as well as at a...