Permission denied despite appropriate permissions using PHP

I'm trying to read a file in PHP and I'm getting a permission denied error although everybody has read access to the file.

The PHP code:

$config=file_get_contents('/opt/jenkins/home/config.xml');

The error:

Warning: file_get_contents(/opt/jenkins/home/config.xml): failed to open stream: Permission denied in [...]

The filesystem permission:

There is a symlink pointing /opt/jenkins/home/ to /var/lib/jenkins and everybody has read permission on the symlink, actual folder, and file.

$ ls -lh /opt/jenkins/
lrwxrwxrwx 1 sysadmin sysadmin   16 2011-08-04 08:12 home -> /var/lib/jenkins

$ ls -lh /var/lib/ | grep jenkins
drwxr-xr-- 6 jenkins adm     4.0K 2011-08-04 10:04 jenkins

$ ls -lh /var/lib/jenkins/config.xml
-rwxr-xr-- 1 jenkins adm 3.9K 2011-08-04 10:05 /var/lib/jenkins/config.xml

Apache configuration

Configured to folllow symlinks (Options All). Adding a Directory directive for /var/lib/jenkins/ makes no difference.

<Directory /opt/jenkins/home/>
        Options All
        AllowOverride All
        Order Allow,Deny
        Allow from All
</Directory>

Additional info

Whether I use the path through the symlink ("/opt/jenkins/home/config.xml") or the real path ("/var/lib/jenkins/config.xml") I have the same problem.

apache2 version=2.2.14-5ubuntu8.4
php version=5.3.2-1ubuntu4.9

Any idea as to why I'm getting the error?