Friends in Servers see Error Signs everywhere?

I am hosting a server on Garry’s Mod so some of my friends can play and build things together and I have quite a few things on my server that they claim they see as error signs. At first, I thought it was simply because they couldn’t read the things in my addons folder, but now it’s actually things that are built into the game, like buttons or certain objects. I have all of my ports forwarded (I assume correctly since the server works), and before I turn the server active I type in “heartbeat” and “sv_lan 0” in to the console.

That you guys know of, is there anything you can tell I’m missing? I have friends on both Mac and PC and they’re receiving the same problem. If you need me to run diagnostics or check anything, I’m fairly savvy on both OS’s so I should be able to help you diagnose my problem.

Also, if there is a thread that already has this solved, I apologize. I’m new and can’t use the search function, so just link me to that and I’ll let you be.