why is no motion is occurring between key frame? I've set two keyframes for an image to move on the y axis. Hopefully this can be seen in the screenshot i've shared: 

however on play back the picture is in one position set by the first keyframe and without gradually moving on the y axis it just jumps to the new position on the second keyframe?
How can I I change this ?

Many thanks
Hm, from your screenshot I see, that your keyframes are the same (gray line between them), so I except no motion between them. 

But why one frame changed? I think it just cashed, and if you press "Refresh sequencer" it resorted to it actual (no-animation) position.

So make sure, that you put keyframes correctly