[Solved - internal server error] SoftException in Application.cpp:256: File ".. /public_html/index.php" is writeable by group.

We were setting up a development environment for one of our sites for maintenance purposes. During that process, we've copied the Drupal code to the 'dev' folder from live. Everything was set proper, including database, settings.php and 'files' folder. However the site was showing 500 internal server error. When we checked the error log we found the following error:

[Tue Jul 14 07:21:16 2015] [error] [client 122.166.241.99] File does not exist: /home/mysiteuser/public_html/500.shtml
[Tue Jul 14 07:21:16 2015] [error] [client 122.166.241.99] SoftException in Application.cpp:256: File "/home/mysiteuser/public_html/index.php" is writeable by group

This is clearly a permissions error and we checked the file permissions. The "/home/mysiteuser/public_html/index.php" was having file permission '0664'. The default file permission should be '0644'. In order to fix the error we did the following and that worked for us.

Change the file permissions from '0664' to '0644' 

Hope this helps. Please feel free to share your thoughts and doubts regarding this here