after an hour of observation. here's what i got.
im having a DEAD gpu. i wonder what's the problem.

lower your intensity... try 16 or 17
rejects should drop and hash rate will probably increase as well
if you still get sick cards then maybe you pushed your gpu/mem clocks too high
assuming you overclocked your cards
Have you tried using the new xintensity settings? For me, I've found that it offers a higher sense of control over the thread count and you can get misbehaving cards back online without losing as much hashrate on your others if you just want to keep global settings for all cards.