Just upgraded to Plesk 11.5.30 and found out that sending SMTP emails with php pear aren't working anymore with following error message:

mod_fcgid: stderr: PHP Fatal error: require_once(): 
Failed opening required 'Mail.php' 
(include_path='.:/usr/share/pear') 
in /var/www/vhosts/mydomain.com/httpdocs/check.php on line 4 

I know in the new Plesk 11.5 they changed the structure of all vhosts, but the strange thing is that require_once('System.php') placed into the same directory and file is working correctly with no errors and is returning bool(true).

Any hints where I could have a look with this mod_fcgid error when

require_once('System.php')

is working but

require_once('Mail.php')

isn't working?