Error 500 after installer.php

Hi,
I have just installed the plugin.
I had developed my site directly as a subdomain in my host.
Then installed the plugin and created a package.
My idea is to replicate the site in another directory, and make the new one the production environment.

What I did:
1- create package using the plugin
2- copy the installer.php, the zip and the sql file to the new directory
4- Uncompress the zip file (otherwise installer.php would time out)
3- run http://mysite.com/newdir/installer.php from a browser
4- select “zip already extracted option” and continue
5- select proper DB name and user and continue
6- select proper final options
7- In the “final steps” screen it seems everything is ok
8- click on “site login” and get the following error:

500 Internal Server Error
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, [email protected] and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I did sone search ion my CPanel, and found the following in the error log:
SoftException in Application.cpp 261: File "/path/index.php" is writeable by group, refer http://my.domain.com/path/installer.php

I tried several times with different variations, but still the same error.

What am I missing?

Thanks a lot!
Cristiano P.