They want the recom letters from the persons who has no personal contact with you. It seemed that most of your recom letters came from the persons who knows you very well, that is, your acquaintances, such as your boss, etc, therefore your letters were considered as dependent, not independent. They think the dependent letters would not give an unbiased opinion about your work. You need to get letters from the persons who do not know you at all but your papers, that is, independent letters, which they think can give unbiased opinions about your work. Hope it helps.
Good luck