I had the same problem too. The reason was that a member had posted 5 slightly nude photos. The visibility of these 5 photos were however friends only. 5 photos out of 5000. So I deleted the 5 contentious photos and renewed the request which was then accepted.
So I think you have to check all the content keeping in mind that you have to avoid content that advertisers would not like to associate with, which is not always obvious, it seems like nothing shocks them.