SWEP's not working

Whenever I download a SWEP, I am constantly “missing a model/texture/sound” and I get many Lua errors about not finding a file. I look at the folders and I don’t see any files missing, but I still get the red error signs and the checkerboard texture. WTF is going on? I don’t know if this helps, but the only Source game I own, is L4D.

Sorry if this is a newbish question, but i’m still new to GMod. :stuck_out_tongue:

What SWEPs have you tried?
They might contain CS:S or DOD:S models.

Paste the errors please