Maybe you can help me with this. The url I have paid for, for my wedding forum is this: http://weddingdayjitters.com/ But when I go to the forum this way I only get PSA's in my adsence ads. You can also get to it this way: http://www.websitetoolbox.com/tool/mb/weddingdayjitters/ Ads show up when you enter it this way. Forum has been running for a couple months now.
There isn't any relevant text near the ads for adsense bot to go on, only an image. My guess would be the 2nd url is at least giving adsense some text to read in the url to grab ads, the short url offers nothing. I would advise to place some "H" tags near the ads. Also change your <title> tag to offer more description about the site, that alone might be enough to get relevant ads.