Some Google AdWords advertisers are reporting that their ads are being disapproved due to what is called "Artificial Ad Traffic." There are two thread at Google AdWords Help on the topic.
At this point, no one really fully understands the issue behind those warnings. An advertising policy guideline on Inflating Ad Clicks or Impressions was hyperlinked to by one AdWords helper. Then a Google representative, AdWordsPro, said that this was the correct answer to such a warning.
It says:
Don't promote inflating ad clicks or impressions.Advertising is not permitted for the promotion of inflating clicks or impressions on ads, such as pay-to-click, pay-to-view, auto-surfing, automated ad clicking, and other guaranteed traffic programs.
An "Artificial Ad Traffic" disapproval has to do with the Inflating Ad Clicks or Impressions guideline.
Forum discussion at Google AdWords Help.