Well, I get this message all the time using AdWhirl:
Unable to fill ad request. This is a common situation.
I think it’s from the AdMob network. I also have a couple of other networks (registered yesterday) and I never seem to be getting any ad requests filled. In test mode it does work though. Now is this common and will it pick up?
Turns out it went away after a couple of days. I guess AbMob had to review the application first.