Garry's Mod Startup on Mac

Hi guys!

Recently I bought GMod for my iMac. But, for some reason I can’t start GMod. When I run it, an icon for hl2_osx pops in my dock but after like 2 seconds it goes away. I’m running Mac OS X 10.7.3 (the latest available) and I have a Source-based game (TF2). I can’t start TF2 too, same reason. I’ve read at that Mac users already reported they’re having issues with the startup, but I searched at the GMod Steam forums and Facepunch and I noticed that nobody is talking about it. I’m just posting here to know with there’s nothing wrong with my computer/my game or all the Mac users are having this problem.

Thanks in advance.

What are your mac specs?

I currently have the baseline iMac, which is the first one from the left.