MacBook Pro 15" Dark World Error - Need assistance!

[Bubz]

hello folks,

I am not sure about that error, so I'll just describe it a bit.

I've got a MacBook Pro 15", 2.2 Gh i7, AMD Radeon HD 6750M (1 GB GDDR5). Steam was installed soon and gmod plus hl2+ep1+ep2, css and team fortress 2 for the content.
When I tried to join a rp server first, it gave me a "couldn't CRC map" error first, so I manually downloaded the map and dragged it into the gmod map folder. Then it worked.

I can just see a very dark world around me, if I activate my flashlight, I can see a bit more, but it's like you turn up the contrast extremly (very warm colours).

What error might it be? I already changed gamma value in settings, so I am a bit helpless.
Thanks a lot.

The map is also Evocity_v33x. This is also just me attempting to help out a friend.