Topic: can't upload image

I can't upload images!! When i tried it says "The image was saved.
The preview thumbnail was created." but can't see any change.No thumnail, too.  I can upload the same photo in other gellery though....
Please help me if you have any idea what is happening!!
Thank you for your time to read this for me.
my home page: www.photo-by-yusuke.com