I’ve had the same problem as OP and apparently my processor doesn’t meet the Mac Beta requirements. However I was able to play GW2 Thursday and this entire problem started Friday. Had the same issue with getting an error that I didn’t pay any attention to because I thought that I wouldn’t need it. The client won’t let me log in or type anything or click and disable/reenable anything, and to quit it I need to force quit it.
Though they said it doesn’t meet requirements, I also asked if anything had changed this Thursday/Friday that would result in my Mac processor not working anymore. Apparently nothing has changed at all, and the requirements have been the same forever. My game ran fine before, doesn’t work anymore now, and I just recently got back into GW2. So what gives? I have my Mac fully updated to OS X Yosemite by now, and the client problem occurred before updating and still persists afterwards. I’m not buying a new computer for just one single game.