i experience the same problem when using booleans sometimes.
here's a few things that might help get around this:
--select all the verts of your object and use the Merge Vertices tool set to like .001 for distance to make sure all the verts are connected correctly.
--try using Polygons-->Cleanup just in case something unwanted is on the model.
--after you try a boolean and it fails, look in the Script window and it will tell you why.
--try selecting the faces of your main object that will actually receieve the new detailing, and extract them from the rest of the model. this worked for me one time. afterwards just join it again if you need to.
hope that helps, i know it can be frustrating.
Car-maker.
Check out my releases for
RACER.
see the WWW button