Hi Rick, it's due to changes that Apple made in how multi-monitor works, the toolkit that Moi V3 uses to run is still not compatible with those changes.

You can solve this though by changing an operating system setting as described here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=8101.6

MoI v4 will solve this and won't need the setting change anymore.

- Michael