I would have asked if you had the trim down far enough, but the above post hints at that. I would guess that if the dx7 throttle was allowed to be lower, that would have the same effect as lowering the trim. I don't have a dx7 so I can't help there.

People using the stock tx have the same problem when they up the trim past the middle while flying, then change the battery and the rx will not arm because it thinks the throttle is on a little.

Mike