GTA: San Andreas for mac took 3 hours to download via Steam. Once it finished downlpading, I quickly clicked 'Play' in Steam. Darn thing won't even start

All I got was a quick notification saying Steam is peparing to launch the game then suddenly this:
Application load error 5:0000065434
I'm frustrated to say the least.
Any ideas what could be the cause & what's a fix for it? FYI, I'm using a mid-2011 iMac 27" i5 with 4GB RAM running OSX 10.7.3.
If it's worth anything, just prior to purchasing the game on Steam, I uninstalled the GTA: San Andreas version I got from the Mac App Store by clicking on it's icon in Launchpad then clicking the cross when it appears. Is that enough to delete all previous game data? Any folders I need to specifically go to to delete all the previous install data? It might be the reason why the error is popping up in the Steam version of San Andreas.
Any help appreciated!