You have a .htaccess file in /admin, right?


So ... try an experiment.

1. make a backup copy of your /admin/.htaccess file. Store it in a safe place.
2. edit the /admin/.htaccess file, and add this to the very bottom:
Code:
  SecFilterEngine Off
3. Save the file and upload it to the server ... again, this is ONLY the /admin/.htaccess file
(only in the ADMIN folder ... not in any other place)

Now do your edits work?

If so, then it's a configuration issue related to mod_security that's causing your problems.