Using Virtualbox In Full Screen On The Second Monitor

When i upgrade my Ubuntu 11.04 to 11.10 , i had a problem with my virtual box . Suddenly my guest OS became in the first monitor when it full screen ( my laptop monitor) not in my 17" LCD monitor.

Actually i run a dual set monitor for my laptop and i want guest OS run full screen on second monitor.

To make it full screen on the second monitor, after entering full screen mode with the guest OS,
hover over the Virtualbox hidden menu at the bottom of the guest OS.

On View > Virtual Screen 1 > Use Host Screen 2
This will make the guest OS shows up in the second monitor when using full screen mode.

I get this tip from : http://tipstank.com/2010/06/04/virtualbox-full-screen-second-monitor/