Can't insert image into post but the image gets attached with the post

Hi, I am using wp 3.1 for my blog. Last night I did a posting and successfully inserted images like usual. But this morning, when I was doing another post suddenly I could not insert any images. I could upload but could not insert it into post. However the image gets attached into the post and it was shown as featured image. When I tried to insert the image it was said the page was not found and I was suggested to do search. Can anyone help me with this? Thank you.