What is the combination of your cards and the hash rate?
What is the difficulty value?
For my 8 GPU 7990+7970 rig (5.6MH/s), the difficulty is 510 at the moment. Some times, it is 1000.
The total rejection rate is 8.9%. It is usually 1%. So maybe it is coin specific.
I have 1 r9 290x from Sapphire, puts out about 904kh/s with stock cooler and a little tweaking. I use cgminer.
What are expiry, scantime, and hotplug?
(btw if you could help me figure out why bfgminer crashes my computer, there's 25 pxc in it for you

)
This is my cgminer config:
"intensity" : "20",
"vectors" : "1",
"worksize" : "256",
"kernel" : "scrypt",
"lookup-gap" : "0",
"thread-concurrency" : "32765",
"shaders" : "0",
"gpu-engine" : "0-0",
"gpu-fan" : "0-100",
"gpu-memclock" : "0",
"gpu-memdiff" : "0",
"gpu-powertune" : "0",
"gpu-vddc" : "0.000",
"temp-cutoff" : "90",
"temp-overheat" : "86",
"temp-target" : "83",
"api-mcast-port" : "4028",
"api-port" : "4028",
"expiry" : "120",
"gpu-dyninterval" : "7",
"gpu-platform" : "0",
"gpu-threads" : "1",
"hotplug" : "5",
"log" : "3",
"no-pool-disable" : true,
"protocol-dump" : true,
"queue" : "1",
"scan-time" : "30",
"scrypt" : true,
"temp-hysteresis" : "3",
"shares" : "0",
"kernel-path" : "/usr/local/bin"
(p.s. lol, litecoin is the most profitable coin to mine right now?! alt cleansing in progress, beware.)