Virutal Box - Setting > System > Base memory greyed out

Hi All,
A friend has Ubuntu 14 desktop as the main OS and is running XP in the Oracle Virtual Box.
We want to increase the RAM available to XP but that setting is greyed out in the VM manager.
XP is definitely not running (that can cause this) as we rebooted the system before trying.

Any other ideas?

thanks. Nknwn