Smalltimer: I got 2 R9 280x GPUs running on a xubuntu box (ran for 2 days without any problems). When I tried to fine tune the settings sgminer started crashing the system. I narrowed it down to different settings for different cards (trying different settings on each card to see which is better). SGminer did not like that. Try the same I=16 setting on all cards (one parameter, not the same value for each card), and see what happens.

I also just noticed that you do not have a valid User name (field is blank). Did you blank it out in the pic? It should be your bitcoin address.