have one of these that ran fine for a couple years now it wont duplex from doc feed, duplexes fine from glass or on prints. switched dadf and same result. all sensors test fine. firmware issue maybe? when it runs docs through the feeder it calls for jam at last page because it's not getting paper fed back in for side 2 so it knows it's supposed to duplex. have lots of these out and have never seen this. thanks--tuey