Check 1, 2 and 3 were all fine.

/includes/languages/english/html_includes/define_main_page.php has permissions:
-rw-rw-rw- 1 shootiel shootiel 1427 May 24 12:36 define_main_page.php

Are there any folders/files you need permissions of?

(Again the strange thing is that this was working fine up to a few hours ago and then bang - it stopped)