Portal errors

I recently got an portal 2 gun addon, but the portals don’t appear correctly, I don’t have a picture, but when I shoot the portal, it appears with the correct width and height, but it is black and has the portal outline inside of it. The console is telling me that I need to recompile the portal model, how would I do that? I also don’t have the game, I’m using a content pack that I downloaded.