Try validating the game's cache first. Then you can try unsubsribing from every workshop item and manually deleting everything QL related in your local workshop directory.

One day, I suddenly had the same issue. And nothing helped: Rebooting, deleting and reinstalling the game from scratch... yet the problem persisted. A friend of mine and I even compared the game files bit for bit. They were identical, yet I could not join his server due to this error.

I wrote with the Bethesda support and one of their instructions has fixed the problem for me: Performing a clean Windows boot. Here are the instructions: https://support.microsoft.com/en-us/topic/how-to-perform-a-clean-boot-in-windows-da2f9573-6eec-00ad-2f8a-a97a1807f3dd

Make sure to NOT disable the service "Steam Client Services". This is the only service that you have to keep enabled.

With a clean Windows boot I was finally able to join my friend's server. It get's better: Even after returning to a normal Windows boot, the problem has now disappeared magically. The error is gone.