Performance problems

[wacher]

Hi,
I got a little performance problem and I need advice what to do
Platform:
Old hp computer
Core 2duo E4500@2,5Ghz
3Gb RAM
Motherboard Ms 7336 ver1
Windows Vista 32bit.
Newest Ati drivers
Club 3D 7950 @1000/1300

Max performance without hw errors is ~250khash.
Setting Im ussing
--failover-only  -I 12 --thread-concurrency 8000 --gpu-powertune 20
For -I max is 12 without errors.
thread-concurrency is max 8k or I get error like bellow
http://imageshack.com/a/img197/9383/k74l.jpg

What can be the problem?