I have a high count polygonal model and I 'carved' out a piece via booleans-worked fine.
When I do another (same kind) boolean on it all I get is an empty node!
[I have deleted all histories and also tried 'clean-up' on the models]
I remember someone telling me once that the resulting model may actually be there but you can't see it...I can't remember 'how' to see it. (if that is actually the problem)
Booleans (and I go to my grave on this except for 1 situation) won't fail if the following conditions have been met
1. No non-manifold geomtry
2. Are being used in polygon to polygon only interference.
3. Actually to have interference.
4. Normals are consistant for both objects in boolean.
Now the 1 situation I refer to above I don't actually know about except that "Jooja" over at Highend3D. Has mentioned that he does know of 1 situation where all the normal conditions are met yet the boolean will fail but it's some tricky wierd thing that he won't let anyone know about for some reason. I don't know what that is as I've used Booleans for everything and as long as each step in the boolean process is cleaned up and a user truely understands what non-manifold geometry encompasses; it will work.
Good luck. If you can't get it to work, post it. I'd be happy to show you why.