Adbrite Help, Impressions But No Dollar

I signed up to Adbrite the other day reluctantly (I already use loads of other networks but thought I could make a little bit extra with Adbrite)
I set the price to beat as $0.40 and used adsense as my alt ad.
So far I’ve had 1300 impressions (should be more) and zero earnings. Yet I’ve seen several ads appear. Shouldn’t I have earned just over $0.40? And if not then why didn’t they display my alternative adsense ad?
Is it a CPC thing? If so can I turn CPC ads off?

See original post by skaterkee