Problem

When you save file content or Instant Update content, it isn't saved (and your files are writable (CHMOD 777)).

Solution

It seems that you have mod_security with very high security policy turned on. Unfortunately, only solution is to turn it off.

If your server is installed as server module, and not as CGI module you could try to create blank text file, name it .htaccess and place it in your website root folder, and place following lines in it. If such file already exists, just append following code at the end of it:

<IfModule mod_security.c>
SecFilterEngine Off
SecFilterScanPOST Off
</IfModule>

Otherwise, if PHP is installed as CGI module create blank text file, name it php.ini and place it in your website root folder, and place following lines in it. If such file already exists, just append following code at the end of it:

FIXME (to do)