It happened on my old computer, now its on my new one and it just says "A un-expected error happened and ROBLOX needs to quit. We're sorry!"
I doubt I will get any help on this.
I'm not a pro but, did you check if your computer was free from anything that was preventing you to start the game, does your internet have some sort of problem, or my most concern, was the website under maintenance? Hope this helped it bit..