guiminer Verification failed and cgminer crashed,what's the matter?

[mithiril]

My card is : HD6850
STREAM SDK is :2.5.6

guiminer log is as below:
 
2013-08-18 12:01:08: Listener for "Default" started
2013-08-18 12:01:08: Listener for "Default": 18/08/2013 12:01:08,  need more than 1 value to unpack
2013-08-18 12:01:08: Listener for "Default": 18/08/2013 12:01:08,  need more than 1 value to unpack
2013-08-18 12:01:08: Listener for "Default": 18/08/2013 12:01:08,  need more than 1 value to unpack
2013-08-18 12:01:08: Listener for "Default": 18/08/2013 12:01:08,  need more than 1 value to unpack
2013-08-18 12:01:08: Listener for "Default": 18/08/2013 12:01:08,  need more than 1 value to unpack
2013-08-18 12:01:08: Listener for "Default": 18/08/2013 12:01:08,  need more than 1 value to unpack
2013-08-18 12:01:09: Listener for "Default": pit.deepbit.net:8332 18/08/2013 12:01:09, started OpenCL miner on platform 0, device 0 (Barts)
2013-08-18 12:01:09: Listener for "Default": pit.deepbit.net:8332 18/08/2013 12:01:09, checking for stratum...
2013-08-18 12:01:10: Listener for "Default": pit.deepbit.net:8332 18/08/2013 12:01:10, using JSON-RPC (no stratum header)
2013-08-18 12:01:25: Listener for "Default": pit.deepbit.net:8332 18/08/2013 12:01:25, Verification failed, check hardware! (0:0:Barts, 34254ad0)
2013-08-18 12:01:26: Listener for "Default": pit.deepbit.net:8332 18/08/2013 12:01:26, Verification failed, check hardware! (0:0:Barts, 360caee4)
2013-08-18 12:01:36: Listener for "Default": pit.deepbit.net:8332 18/08/2013 12:01:36, Verification failed, check hardware! (0:0:Barts, 9fb753eb)
2013-08-18 12:01:55: Listener for "Default": pit.deepbit.net:8332 18/08/2013 12:01:55, Verification failed, check hardware! (0:0:Barts, dd2acbdd)
2013-08-18 12:02:01: Listener for "Default": pit.deepbit.net:8332 18/08/2013 12:02:01, Verification failed, check hardware! (0:0:Barts, ed398d6c)
2013-08-18 12:02:04: Listener for "Default": pit.deepbit.net:8332 18/08/2013 12:02:04, Verification failed, check hardware! (0:0:Barts, dcd2df62)
2013-08-18 12:02:07: Listener for "Default" shutting down

what's the matter?