Hi Michael,
I stumble again and again to new problems.

As long as I boole out only 1 or 3 spheres at once, all works fine.
As soon as I select all spheres and try to boole them out, the main object dissapears.

Too much calculation for my MacPro (28 gig Ram, 8core 3,2 ghz)
or too much calculation for MOI?

Sorry for the constant annoying questions!

Mike