Do you have any of the EPN creatives on your site(s) that carry a tracking code? If not, you won't see any impressions.
KGL, You can also add a tracking pixel on your pages by using the link generator. Go to EPN tools, link generator and create any link you want. You will be given the java script, html and impression pixel codes all on one page. I created one for every website and also use wp-stats for the blogs and google analytics for all sites. You can also track your websites using awstats with your web host. I have read on the other forums that some people have having trouble with tracking when using the banners. Hope this helps you out some!