If you unlearn skills in human form it will also unlearn the dragon skills (including the default point in FireSphere, IIRC). Could that have been the problem?
If not, some people have had issues assigning or changing the hotkey spells (though not specifically for dragon form, that I recall). From a couple different topics:
How are you assigning skills to quickslots? There are a couple of ways:
1) Keep the numerical key on your keyboard pressed for +- 2 seconds.
2) In pause mode, right click on the slot you want to quickmap.
3) In the skill screen, drag the skill icon to the quickslot.
Which of these options are you using and can you try the others?
It'd help which skill you were trying to hotkey because, not all skills are hotkeyable. For the ones that are, you Left-Drag the skill into one of the slots and click when the slot lights up. From my experience, those slots don't become active (light up) unless you aim towards the very bottom of the slots. I think they did that so that you couldn't accidentally move something out of the bar. They must never have heard of "Locking" the action bar.
I've had that memory issue on a couple game I've replayed. It is annoying when you can not get something to work, and then finally check a walkthough and discover that you remembered step 1 and 3, but forgot 2.
