Activities: Checklist mod_checklist Internal Server Error

Installed Checklist activity and mod in Moodle 2.5. Can edit settings but when click to open to enter checklist items get Internal Server Error. Cron set for 8 minutes.
Error log shows:
[Mon Oct 07 09:36:30 2013] [error] [client 62.20.201.197] File does not exist: /home/pplteori/public_html/500.shtml, referer: http://www.pplteori.se/moodle20/course/view.php?id=15
[Mon Oct 07 09:36:30 2013] [error] [client 62.20.201.197] SoftException in Application.cpp:256: File "/home/pplteori/public_html/moodle20/mod/checklist/view.php" is writeable by group, referer: http://www.pplteori.se/moodle20/course/view.php?id=15
[Mon Oct 07 09:29:39 2013] [error] [client 62.20.201.197] File does not exist: /home/pplteori/public_html/500.shtml, referer: http://www.pplteori.se/moodle20/course/modedit.php?update=33&return=0&sr=0
[Mon Oct 07 09:29:39 2013] [error] [client 62.20.201.197] SoftException in Application.cpp:256: File "/home/pplteori/public_html/moodle20/mod/checklist/view.php" is writeable by group, referer: http://www.pplteori.se/moodle20/course/modedit.php?update=33&return=0&sr=0