Koffee, I'm not quite clear on whether you're able to lock the locking wing on the bag against the rack. Are you? And the problem is that the wing turns when you ride and the bag falls off? Or aren't you able to lock the wing at all to begin with?

If you are able to lock the wing, you might try simply tightening the bolt head holding the wing against the bag. With more friction, the wing won't turn when you hit bumps.

If you're not able to lock the wing, you might try first pushing the bag horizontally against the rack, after the bag is on the rack and the upper hooks and the bungy are in place. The bag will sag a bit outward, normally, so pushing it as flush against the rack as you can may allow you to turn the wing more easily. It may also allow you to use the longer side of the wing, where you might have been able to use only the shorter side before. If you find that pushing the bag against the rack allows you to use the longer side of the wing, where you couldn't use the longer side before, then your bag will stay secure on the rack.

If you can't lock the wing, whether you push the bag against the rack or not, you'll have to move it. Well, you or Arkel or someone will have to. It's a bit of pain to borrow a drill, perhaps, but you'll have to spend time anyway with the Arkel guys at the bike show.

I've been very happy with the Arkel hardware, myself. It's solid as a rock (though sometimes I have to push the bag against the rack to swing the locking wing into place). I've never had a wing unlock when I rode, much less a bag fall off. The hardware's simple, too, so the bag is very easy to get on and off. If repairs are necessary, they're about as simple to make as they can be. In fact, I've like the Arkel hardware so much I bought it separately and upgraded some old bags with it.

Good luck with this...