I only get this error when running oxide. I have no idea what it means or how to fix it because I have tried remaking my entire server from scratch and I still had the error. I believe this is an oxide issue.

Having the same problem.

That is not an Oxide issue, but rather likely from a plugin or extension doing something with building grades. Oxide does not do anything with buildings itself. 

No plugins are on; I just installed oxide by itself.  The server works fine without oxide though.

Merged post

Reinstalling SteamCMD and all associated folders along with deleting the entire Rust server fixed the problem, just had to reinstall Rust and the plugins after.  Hope this helps Joe.