I've actually been back and forth via email with them today and they are refusing to pay even though I have served their ads for six months. They said they flaged the site back when I first started but oddly enough they kept serving the ads.
The first email said "you are serving more than one popup" and told me to review the rules. I did so and in the rules it says no more than two. So I pointed this out and told them it's not about the money now it's the pricipals. They responded back with yes it is the priciples and when our advertisers follow the rules they get paid.
My response was that I didn't think they had a problem when they billed their advertisers and I'm sure they didn't put much thought into cashing the check.