Date: Mon, 13 May 2013 12:51:55 -0400
From: ken <gebser@mousecar.com>
CC: help-gnu-emacs@gnu.org
What does Emacs say if you type this:
M-: major-mode RET
in the buffer that visits this file you aren't allowed to edit?
image-mode
That explains everything, doesn't it? Your file has a file-name
extension that matches some image file, so Emacs enters the Image mode
for it, and doesn't let you edit images (because image-editing
capabilities are not yet part of Emacs).
Solution: remove that extension from auto-mode-alist, and Bob's your
uncle.