Define Mainpage errors

[Anonymous]

When I try to edit the text on the main page by using the WYSIWIG editor, I'm getting the following error:

ERROR_FILE_NOT_WRITEABLE
mainpage.php

Click path:
Admin > Catalog > Define Mainpage

I cannot find the file named mainpage.php. I have modified the permissions on the following pages to chmod 777, but the problem continues:
/admin/define_mainpage/php
/catalog/templates/main_page.tpl.php

Is there a fix for this?

[michael_s]

mainpage.php needs to be CHMOD 777 - /includes/languages/english/mainpage.php