Its not that its overclocked but its overclocked without the rest of your script being set up accordingly.
Post you GPU specs and your CGminer scrypt and I or someone else will try to assist.
An unstable overclock alone can give you errors. OP try lowering your intensity, also post whatever post your cgminer settings that you are using.
i did reset my clock settings, and tried to run with GUIminer now ia m having 220 khash and site say it same. i think i fixed it o.0 but i wanted to sue it clocked :S
You should overclock in smaller increments of 10 or 20Mhz also when it is unstable if you can raise the voltage that helps stabilize it but it definitely makes cards run much hotter.
You can see default setting of my Clock above post.
I did clock like this ;
950 core clock
1300 mem clock
%100 fan
can you recommend me any settings*
I wouldn't recommend 100% fan speed that will wear them out pretty fast try 75% or lower. Find a sweet spot where your temps aren't going up anymore and your card isn't too hot. You should try 1000 core clock and 700mhz on the memory see if that helps. I am running my 7950s at 1050 core/699 memory and I get 550 Kh/s
Maybe try this also at normal clocks: intensity 12, , threadconcurrencyc: 8192, g: 2, lg: 2, ws: 256