Every time I start GMod i get this error message :SteamUser() returns NULL!' help!

Ok, so my Garry’s Mod was working fine then i went off for a bit and came back on and it gave me that error message. I got counterstrike after the error messages and it made no difference, i’m on a mac mini. I know macs are terrible for gaming but im not a big PC gamer. I have unistalled it and reinstalled it but it made no difference, i’ve deleted all my addons but nothing seems to work. please help me!

[editline]30th June 2012[/editline]

Just ignore this, i put it on wrong thread. I’m very sorry.