Failed to load sound?

I got this weird error in Hammer Source SDK. It won’t load a song. When I test the song out on the entity it works, but when I startup my map and try it, it’s just saying:
Failed to load sound (file name and stuff here) file probably missing from disk/repository
could someone please help me?

I’m getting something akin to this myself; and I know I have everything properly scripted.
Help some brothers out?

Not sure where else this can go but this is
Garry’s Mod > Garry’s Mod Discussion > Help & Support.

Oh and Source SDK doesn’t even work for me… :confused: I start it up and It crashes.

Okay I got it. I downloaded Pakrat and loaded the BSP. Then I added the song into the BSP and saved it. I used WAV, so I’m not sure it’s the same with MP3