cannot delete old thumbnail image

Hey, guys. I'm trying to update some thumbnail images throughout my gallery and this one is stumping me. I'm trying to delete a thumbnail of an old cel I added in 2002 and every time I delete it, it mysteriously comes back to life again, over and over and over again. haha I can't get rid of it and replace it with a new, larger thumbnail. Any ideas??

Heh, I've got a similar problem, only that my thumbnail disappeared (it was a special one I'd made that said spoiler since the image itself was, in fact, a spoiler) and I can't upload one. I can't even get the thumbnail generator to work. So I have a broken image box for a thumbnail. >.