Please have a look Release Notes for Parallels Plesk Panel 11.0. May solve your problems.
http://download1.parallels.com/Plesk/PP11/11.0/release-notes/parallels-plesk-panel-11.0-for-linux-based-os.html
Thanks
Have you configure sub domain for voice.mydomain.co.uk ?
If you don't have DNS server then ask to your provider for DNS entry. Then ping voice.mydomain.co.uk if success then it will be work. have fun..........
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SakibS