This is a problem I had myself. It is another example of the lazyness of the designers.
You have to click on the bag. The bag opens and now you have to DRAG the inventory window to the right. Now you will see the window of the open bag and you can drag crystals from the inventory to the bag.
So basically the bag window is hidden behind the inventory screen...
Greetz,
Zed <img src="/ubbthreads/images/graemlins/alien.gif" alt="" />