Sometimes when we update our content Garry's Mod can take a while to catch up. If you see missing pink/black textures or receive a "Missing content message ". Follow these steps to fix it:

1) Unsubscribe from the CHRISTMAS CONTENT pack:
steamcommunity.com/sharedfiles/filedetails/?id=566075167
2) Run this command in console: menu_cleanupgmas
4) Delete all files in garrysmod/downloads/server/
3) Restart the game and re-connect to the server the updated content will be downloaded automatically.

Enjoy!