need help with a lighting problem

ok so iv reinstalled gmod 2 time now but but still keep getting this bug with what i think is the lighting this is in stop it slender but i also get it on ttt anyone know what it is and how i can fix it

http://cloud-2.steampowered.com/ugc/921273757974392885/D33F7B7EFB173BB4D674C55CE78DFAD02BFBE381/

Try updating your graphic driver.