Re: "Text is read-only"... except it isn't... or shouldn't be

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 13 May 2013 05:47:46 -0400
> From: ken <gebser@mousecar.com>
> 
> A file which I've been opening in emacs and editing for a few years in 
> emacs suddenly with emacs version 22.1.1 became read-only.  I open it, 
> can navigate around in it (though the cursor/mark isn't visible), but 
> when I try to edit it, I'm not allowed.  I get a message in the 
> minibuffer saying, "Text is read-only".  The beginning of the modeline 
> is "-u: --".  I can open this same file in vi and edit it (as the same 
> user) without any problem at all.  I don't have this problem with any 
> other file I edit in emacs, just this one.  The OS is linux, kernel 
> version 2.6.18.384, and the permissions for this file are 664 and I am 
> the owner of the file.  If I change (i.e., mv) the name of the file to 
> something else, emacs behaves normally and lets me edit the file just 
> like any other file.  So I'm pretty sure that the problem is that emacs 
> has a problem with the file name and thinks I shouldn't be allowed to 
> edit it.  How do I turn this behavior off?

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?