A winey, wet cardboard, papery, rotten vegetable/pineapple, sherry or baby diaper type of aroma or flavor is a sign of an oxidized, stale or old beer. Over time the symptoms get worse. Any oxygen that is introduced in the brewing process will eventually show up. Temperature accelerates the process of oxidation.
It is very important to keep oxygen to a minimum in all stages of the brewing process (except when pitching yeast). Store your beer cold to slow down the effects of oxygen introduction.