Are you using photobucket? I use photobucket for a free host, then copy the "IMG" url into the sig box, then press update sig. But take note, you will need to resise the pic before uploading to photobucket.
www.photobucket.net
But if thats too much for ya, its pretty simpl , it could be the type of file youve saved it as. Try saving it as a jpg file first. Then try again.
Yep, as Sunflower suggested, from the properties of the URL you are trying to post, it looks like you might have deleted or moved the pic from photobucket OR deleted it from your computer.
Try again