Need help regarding a server.

Hello! I run a Garry’s Mod server through SteamCMD that my friends and I play on. We usually just play Murder, Prop Hunt, and Hide and Seek. On some maps however, we can walk through things that should otherwise be solid. (For example, on ph_library we can walk right through the bookshelves.) Is there anything we can do to fix this?

You need CS:S installed and mounted on your server. If you host a server for your friends, you can just use the in-game server.