Hi all. Just had this problem with my Captivate out of the blue this past weekend. Happened right after taking it off the charger over night.  I've had this phone since Jan. with no problems. Spent all day yesterday speaking w/ AT&T & Samsung reps. and finally doing a hard reset to no avail.  After reading Foxbat121's discussion of the mini USB port pin issue I took the phone out to the garage and blew out the port with compressed air thinking maybe some debris might be shorting the pins and causing the phone to think it was connected to the dock. It immediately fixed the problem! I would think an aerosol can of electronics cleaner or such might work as well. Can't believe it was such a bizarre problem. Hope this helps, Bill