I cannot tell anything from the images you provided, but from your description of what you did, you appear to have made an error. If you added the graphics into two frames and then created a symbol out of each of them, then those are two different objects. To do a motion tween you have to have the same object at both ends.
Try creating the symbol first, then place that same symbol in the two keyframes.
Thanks Ned. Still not working. Here's what I did.
1. Opened a blank Flash actionscript 3.0 file.
2. I imported the vector graphic to Stage.
3. I converted it to a symbol.
4. I inserted a new keyframe at #40.
5. In keyframe #40 I then dragged the symbol over to the right.
6. I clicked between the keyframes (around frame 15 or so) and went to Insert-Motion Tween.
It does the same thing. No movement from 1-39 and then jumps over at frame 40.
Looks like you're running into the difference between new motion tweens, and classic ones in CS4.
Flash no longer interpolates between two separate instances, in new tweens you animate a single object. There are numerous benefits, you can read about them here: http://flashthusiast.com/2008/09/22/the-new-way-of-tweening-in-flash-cs4-or-new-motion-in- flash-cs4-makes-your-animations-better-faster-stronger/
So to animate your instance, instead just move the instance at the end of the tween span you create, instead of a the next static frame -- a keyframe will be automatically inserted for you.
More information on migrating from old tweens to new one can be found here: http://www.adobe.com/devnet/flash/articles/motion_migration_guide.html and on the blog here: http://flashthusiast.com/. A complete guide on animating in flash is here: http://www.adobe.com/devnet/flash/learning_guide/animation/.