You might seen blank adsense ads. There are a couple of reasons for this.
First, you may be displaying too many ad blocks. The limit is 3 content ads and 1 link unit ad. If you are displaying too many ads while there are only little contextual advertisers, you might end up with blank adsense ads.
Second, there might be no advertisers for the keywords in your page’s content. Either you get them PSAs (Public Service Ads) or a blank ad block.
There are no solution, if there are not enough contextual advertisers. You can try changing the website topic, so that it can match contextual advertisers.
