An unregistered panel is a display panel that you have added to your site profile but which has not been registered to any device. Having unregistered panels is bad because they result in a portion of your advertising income being refunded to advertisers due to the fact that advertisers bid according to the number of fully operational panels.
How do I register a panel?
Panels are registered at the time you register a display device. This is essentially when you click "Show ads" on the "My Sites" dashboard to set up the device and begin showing ads
How is the refund to advertisers calculated?
The refund to advertisers is calculated by dividing the winning bid by the total number of listed panels, and then multiplying it by the number of panels that successfully displayed advertisements for the full timeslot. For example, if you list 2 panels on your site profile and only one displays ads for the full hour, half of the advertiser's bid will be refunded back to them.
What can I do about unregistered panels?
.Remove them from you site profile, or register them to devices that will display ads.