php Error, stoping a section of a site working...

[QuantumX]

Gents.

I've been stumped on a problem for the last few days, and was hopeing to get some help here.

Anyway i'm running Plesk 8.1. The problem is one of the domain on my server is trying to run a bit of webbased software that seems to install ok and create all the mysql db enteries and files, which i have confirmed howvere, when they try to browse to the page its blank, just a big white screen with no error messages.

Anyway I checked within the logs and found the following:

[client x.x.x.x] PHP Warning: main(db.php) [<a href='function.main'>function.main</a>]: failed to open stream: Operation not permitted in /var/www/vhosts/sicarri.net/httpdocs/ZelotKB/common/index.php on line 2
[client x.x.x.x] PHP Fatal error: main() [<a href='function.require'>function.require</a>]: Failed opening required 'db.php' (include_path='.:') in /var/www/vhosts/sicarri.net/httpdocs/ZelotKB/common/index.php on line 2
[client x.x.x.x] PHP Warning: main() [<a href='function.main'>function.main</a>]: open_basedir restriction in effect. File(/db.php) is not within the allowed path(s): (/var/www/vhosts/sicarri.net/httpdocs:/tmp) in /var/www/vhosts/sicarri.net/httpdocs/ZelotKB/common/index.php on line 2
[client x.x.x.x] PHP Warning: main(db.php) [<a href='function.main'>function.main</a>]: failed to open stream: Operation not permitted in /var/www/vhosts/sicarri.net/httpdocs/ZelotKB/common/index.php on line 2
[client x.x.x.x] PHP Fatal error: main() [<a href='function.require'>function.require</a>]: Failed opening required 'db.php' (include_path='.:') in /var/www/vhosts/sicarri.net/httpdocs/ZelotKB/common/index.php on line 2
[client x.x.x.x] PHP Warning: main() [<a href='function.main'>function.main</a>]: open_basedir restriction in effect. File(/db.php) is not within the allowed path(s): (/var/www/vhosts/sicarri.net/httpdocs:/tmp) in /var/www/vhosts/sicarri.net/httpdocs/ZelotKB/common/index.php on line 2
[client x.x.x.x] PHP Warning: main(db.php) [<a href='function.main'>function.main</a>]: failed to open stream: Operation not permitted in /var/www/vhosts/sicarri.net/httpdocs/ZelotKB/common/index.php on line 2
[client x.x.x.x] PHP Fatal error: main() [<a href='function.require'>function.require</a>]: Failed opening required 'db.php' (include_path='.:') in /var/www/vhosts/sicarri.net/httpdocs/ZelotKB/common/index.php on line 2

Note: I removed some ip addresses.

Any i decided to check the php code of index.php at line two and found the following.

<?php
require_once('db.php');

the file db.php exists within the /var/www/vhosts/sicarri.net/httpdocs/ZelotKB/common/ directory the same as the index.php trying to reference it.

Which is a writable and accessable folder has far as i can see. (chmod 755)..

I have managed to find reference to restricted access to various folders controlled via a vhost.conf file but i dont see how that is an issues because the folder with the file in is not restricted.

Anyway any help would be greatly appreciated, because i'm stumped!