Treeview imagelist won't load images

Hi all,

I have 2 imagelists for a treeview, each load some images, set up on design time. However, when I ran the program several times, I can't see these images anymore. If I goto the imagelist property and click one of the image buttons (they greyed out somehow), then run the program, images will show for a while, then disappeared. Can anybody tell me why? I also tried to load images at the run time using imgList.ListImages.Add i, "key", LoadPicture("my ico path"), but images won't show even once.

Any suggestion will be appreciated.