Every model from new addons shows only "ERROR"

[tudormese]

I bought the game last week and I only started it today, I opened a sandbox server from the start and all I see are red "ERROR" signs everywhere. I tried to follow a thread that says it would solve this problem, but the first step didn't work, deleting the "cache" folder.
Another step said to fix something trough Options in Multiplayer tab, but the problem is that I don't have any "Multiplayer" tab in the Options menu so I don't know how to continue. Here's the Steam thread that I followed: How To Fix Missing Addons/Textures Or (Lots) of Error Signs/Pink..
And lastly, I tried verifying the game files and reinstalled the game, still same issues...