Failed to open stream - Permission denied

[rafsouzap]

Hello! Can anyone help me with this error? I access the site and returns error 500, and this is the log record.

[Sat Jun 14 04:45:37 2014] [error] [client 192.168.56.1] PHP Warning: require(/var/www/app/lib/core/RPlugin.php): failed to open stream: Permission denied in /var/www$
[Sat Jun 14 04:45:37 2014] [error] [client 192.168.56.1] PHP Fatal error: require(): Failed opening required '/var/www/app/lib/core/RPlugin.php' (include_path='.:/usr$

[iwind]

First, check the file existence "/var/www/app/lib/core/RPlugin.php".
Second, chmod 777 the file to give the PHP permission.