500 internal server error - zendframework - communication error

Question

I am working on one of the website using zend framework on virtualmin(ubunto) Apache server. website was working fine, until I added following lines

$part = $message;
while ($part->isMultipart()) {
    $part = $message->getPart(1);
}
echo 'Type of this part is ' . strtok($part->contentType, ';') . "\n";
echo "Content:\n";
echo $part->getContent();

in this script, which was working fine before adding above lines.

public function showAction(){
        $this->_helper->viewRenderer->setNoRender(true);
        $this->_helper->layout->disableLayout();

     $mail = new Zend_Mail_Storage_Imap(array('host'     => 'mail.abc.co.uk',
                                         'user'     => 'abc.co.uk',
                                         'password' => 'abc'));   

    $maxMessage = $mail->countMessages();

    print_r($maxMessage);
    foreach ($mail as $messageNum => $message) {
        // do stuff ...
        echo $message->subject . "\n";
    }
}

Since the time, I have added the multipart message above loop. my none of script is working on this particular site. Even I have commented out all of above script and only try to run phpinfo() line, but still is say 500 error.

While other websites under virtualmin is working fine.

Following are the errors which i am receiving

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, [no address given] and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

My log file says

[Wed Sep 07 10:01:44 2011] [notice] mod_fcgid: call /home/websites/cms/public_html/index.php with wrapper /home/websites/cms/fcgi-bin/php5.fcgi
[Wed Sep 07 10:01:50 2011] [notice] mod_fcgid: process /home/websites/cms/public_html/index.php(23615) exit(communication error), terminated by calling exit(), return code: 255

Can Anyone tell me please what exactly I need to do to fix this error.

Thanks.