Playback on 30" monitor problem @ full screen

[T_G]

Created a simple test show with just a couple of slides.
When I try to play it back on my 30" monitor, it's now showing right. It's as though it's cutting part of the end of the slide off and wrapping it back around. Also no text is showing, just a big white blank spot on the side of the slide that's not wrapped around.
Play back fine on the 30" monitor if I play it back inside of the Impress program window.

Plays fine thru the same computer on a 24" monitor, on the laptop and on the projector, all are OK.

Big monitor is 2560x1600 pixles. Is there something weird about Impress that it won't play back on this size monitor in full screen?

Thanks
T.O.