Muzzle flash black squares

On my server I added the M9K gun addons and whenever I shoot some of them the muzzle flash is a black square, I tried looking for a resloution everywhere with no luck. Anyone knwo what I can do to fix this?

uninstall pirated css content?

A friend gave me the content pack and the muzzle flash worked before the recent Gmod update.

exactly (pirated) remove it.

Ah, I view pirating as downloading the whole game not content. Also, how come it worked before then?

If you are having issues related to models/materials/sounds, make sure that you do not have any illegitimate content packs installed for games you do not own, such as Counter-Strike: Source.