(AW\Maya4.0\docs\en_US\html\UserGuide\ModelingPoly\ModelingPoly.htm)
Случается такое, когда в месте пересечения объекты имеют "дырки"
"...Boolean operations require THAT THE TOOL AND ORIGINAL SURFACES BOTH BE CLOSED IN THE AREA WHERE THEY INTERSECT. Boolean operations are very sensitive to the quality of the surfaces intersecting....occasionally Boolean operations may fail for topological reasons. The following error message displays:
Cannot perform boolean operations for topological reasons.
If this happens, the objects that were selected before performing the (failed) operation BECOME INVISIBLE.
С наилучшими!