Not a problem
1: Do not just make a folder like Gamemode_CityRPG and then Add to archive. If this was the problem, he would'nt have the current issue
You have to select all the files within that folder using Ctrl and then add to archive.
2: Delete the _MACOSX folder in your addon. RTB 3.5 Does not accept this. I can't help you if your addon doesn't work on macs
3: Delete that .DS_Store file. I have no idea what this is for.
4: Deleting the _MACOSX folder fixes this error too.
5: Solution 1 should fix this. If not, make sure server.cs is coded properly
What? You tell him what files to delete but do not tell him how? Boy, go learn how to help people properly.
Solution/Step 1 and 5 both do not apply because then he wouldn't be having the current issue. It's sorta logic there pal..
Solution/Step 1 is poorly explained.
I'm going to re-write it for you.
1: You created an add-on folder called weapon_gun, now this is just an example. You cannot, CANNOT just highlight the folder weapon_gun and right click send to archive. You have to go in the folder. Highlight all the files and then right click send to archive.
If you do it INCORRECTLY it will look something like this: weapon_gun.zip/weapon_gun/filesarehere
If you do it CORRECTLY it will look something like this: weapon_gun.zip/files are here
Hope that is explained well enough and works.