PROBLEM:

Can't login to Plesk - ERROR: Call to a member function getWebServerPackage() on a non-object (class.ServiceControl.php:76)
YUM wont update - process ends abruptly with the message "Killed"


SOLUTION:

1. Shut down your server or VPS
2. Increase the RAM
3. Bootup your server
4. You may need to clean up YUM, follow this link: http://itmnetcom.ca/ib/knowledgebase/51/YUM-Update-Issues.html


CAUSE:

This is usually caused by a lack of RAM on your server.

I hope this helps.