Publicado originalmente por R. Star?:

That might occure especially due to updates (if there are similar file names, sometimes vmt. changes are not noticed by workshop).
As 8sianDude said, unsubscribing and cleaning cache of addon might a solution. To do that:

1. Unsubscribe
2. Log into g-mod
3. Open console and type "menu_cleanupgmas" (afterwads you might double-check your "...\Steam\steamapps\common\GarrysMod\garrysmod\addons" or "...\Steam\steamapps\workshop\content\4000\2252304893" folders to make sure that there is no more existence of .gma files)
4. Re-subscribe.
5. Profit.

If the problem still occurs, we'll check around sharp edges of pack again, but regardless, on my testing, everything seemed to work fine.