can't set video memory

[ellenfinkl]

I'm getting an error:
Display: Screen page
The virtual machine is currently assigned less than 18 MB of video memory which is the minimum amount required to switch to full-screen or seamless mode.
The problem is that when I go to Display, Screen, the Video Memory setting is grayed out.
Any ideas?
Thanks

[stefan.becker]

You can change Settings only when the guest is not runnng.

[ellenfinkl]

Thanks, that did it.