How to fix a file that's read-only despite showing correct permissions
Try ls -lO to see if any file flags are set.  If it's locked (uchg flag), you can unlock it in either the Finder's Get Info window, or with chflags nouchg "Bad File".  If some other flag is set, use chflags no&lt;whatever&gt; "Bad File" to clear it.

EDIT: The -O flag to la adds another column between the group and size of the files, listing file flags (if any).  Note that flags are entirely separate from extended attributes (what -@ displays).  Here's an example:

$ touch "Normal File" "Locked File" "Invisible, Append-only File"
$ chflags uchg "Locked File"
$ chflags uappnd,hidden "Invisible, Append-only File"
$ ls -l
total 0
-rw-r--r--@ 1 gordon  wheel  0 Feb  4 07:24 Invisible, Append-only File
-rw-r--r--  1 gordon  wheel  0 Feb  4 07:24 Locked File
-rw-r--r--  1 gordon  wheel  0 Feb  4 07:24 Normal File
$ ls -lO
total 0
-rw-r--r--@ 1 gordon  wheel  uappnd,hidden 0 Feb  4 07:24 Invisible, Append-only File
-rw-r--r--  1 gordon  wheel  uchg          0 Feb  4 07:24 Locked File
-rw-r--r--  1 gordon  wheel  -             0 Feb  4 07:24 Normal File


The uchg flag is what gets set if you check the "Locked" box in a file's Get Info window.  BTW, the "hidden" flag only affects the Finder -- the only way to hide files from the command line is to put a . at the front of the filename.