Player disconnecting: ArgumentNullException: Argument cannot be null.

This guy keep on disconnecting with the following error: Gyazo - c34b052e3809cf54d6c20bfb2844a214.png

I've also had another guy disconnect for: Player disconnecting: UnauthorizedAccessException: Access to the path "C:\Program Files (x86)\Steam\steamapps\common\Rust\cfg\client.cfg" is denied.
Gyazo - 7c4e6152fb5266d88f790f319d7cc7d5.png

Any idea how, and is something wrong?

 

Do you think he is hacking / having some files changed? It happens quite a lot, I see atleast a few every hour.