My client crashes randomly sometimes as well when I alt+tab. I run my client in full screen mode, and I run my graphics at less than what my computer can perform (I need a separate hard drive I know :<) but I don't exactly know why my client crashes, it doesn't do it all the time when I alt+tab although I try not to alt+tab because I get this problem now!

Would this be a PC problem or a client problem? It's hard to know which is causing the error. Maybe it's Chrome doing it, I usually load up Google Chrome when I alt+tab.