Only one core working on my 5970?

[JayPhizzt]

I just got myself a Radeon 5970 which will solely be used for mining, but for some reason I'm only able to mine with one core?
I'm using guiminer and I start two clients and choose [0-0] Cypress on one and [0-1] Cypress on the other, but they still only use one core? I get around 320Mhash/s, when I should be getting twice as much
Does anyone know what could be the problem here?
I should also mention that I'm running WinXP 32bit, Catalyst 11.6 and guiminer v2012-02-19.

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[JayPhizzt]

I've made some progress with my issue now. I've installed Catalyst 12.1 and now both cores seem to work, but when I start mining on the second core I get "Verification failed, check hardware" after only a minute or so. What the **** could be wrong? Perhaps I should keep trying different drivers?

[Undef]

Not exactly relevant, but I just finished a crossfire install and had a bear of a time getting them both to run.  In my case, I had an overloaded power rail preventing good power from reaching one card.

Just to be sure water is wet and gravity still works: are you sure you are not having power issues?  Heat issues?  You're not overclocking yet, right?

[JayPhizzt]

Not exactly relevant, but I just finished a crossfire install and had a bear of a time getting them both to run.  In my case, I had an overloaded power rail preventing good power from reaching one card.

Just to be sure water is wet and gravity still works: are you sure you are not having power issues?  Heat issues?  You're not overclocking yet, right?

I have a 650W 80+ Gold power supply, so I don't think I have insufficient power. And I haven't overclocked anything. The only clocking I've done is on the memory which I've underclocked to 500MHz.

[JayPhizzt]

I finally got both cores to work! Switched back to 11.6 and installed Stream SDK 2.1 and now it seems to work. Although, the total speed constantly fluctuates between 400-700Mhash/s.. Shouldn't it be more stable? What could the problem be? Flags?

I'm using these flags at the moment:

-k phatk VECTORS BFI_INT FASTLOOP=FALSE AGGRESSION=7 worksize=128

Anything I should change? I've tried AGGRESSION=11, but for some reason I get a higher Mhash/s with 7?