Fran, if you're moving the dragon in Bryce and not in DS, you'll need to move to the correct frame in Bryce, move the dragon in Bryce, then save the dragon's new position by left-clicking on the + button and choosing position from the menu. Repeat for each frame.

The empty frames in B6 are caused by going back into DS then returning to Bryce. The old animation is deleted but the frames aren't reset so the "new" animation gets appended to the end of the deleted frames. The B6 documentation shows how to get rid of the empty frames in the Working with DS and Poser section.