There is a thread at the Microsoft Advertising Forum where one advertiser is complaining about his ads not being approved in the adCenter console. The issue is not his but rather a delay in the ad approval system.

Ricky Poole, Microsoft adCenter representative, said:

The advertiser said their ads were in review for a week or so with no status update.

So if you have the same issue, post in the Microsoft Advertising Forum.

Forum discussion at Microsoft Advertising Forum.