installare script social engine errore

salve sto cercando di installare lo script social engine
ma mi da questo errore

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, info@altervista.org 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 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.

qual'è il problema? ho gia settato i dati per il database
database.sample.php
ho provato a modificarlo in
database.php ma non cambia nulla come risolvo?

edit
cancellando l htaccess mi da questo problema

Your session configuration is incorrect and could not be automatically corrected. Please set session.save_handler=files and session.save_path=/tmp (or your temporary directory on non-Linux OSes.
For "cache_dir is not writable", set full permissions on temporary/cache

EDIT2
Sono riuscito ad andare avanti ma ora mi da questo problema
Please log in over FTP and set CHMOD 0777 (recursive) on the public/ directory
io ho gia settato i permessi

Nessuno risponde.?