Sony data projector doesn't display desktop

I love my MacBook Pro -it's used all the time in schools, without hassle. However, when I try to connect to a Sony VPL ES1 data projector, the screen resizes (normal and OK) but the data projector shows a completely different desktop image and I can't see a cursor. Presume this is a bug, but is there a work-around I'm missing?
Cheers for any help!