Please explain how you solved the problem.
I have the same problem with Mage.php was not found!
Plesk 9.5.2, CentOS 5.3, Magento 18.104.22.168 installed on domain1.com root, second domain is domain2.com.
I tried all suggestions in index.php:
or full path to Mage.php:
$mageFilename = '../app/Mage.php';
$mageFilename = '/var/www/vhosts/domain1.com/httpdocs/app/Mage.php';
When I try to access domain2.com I get:
../app/Mage.php was not found
/var/www/vhosts/domain2.com/httpdocs/app/Mage.php was not found
The group:owner of Mage.php is: psacln:f_domain1name
When I try to access http://www.domain1.com/app/Mage.php I get:
You don\’t have permission to access /app/Mage.php on this server.
Apache/2.2.3 (CentOS) Server at http://www.domain1.com Port 80
Please attach the .htaccess files and index.php files for both domains.