Hi,
as far as I'm concerned, this could as well be a hyperhtreading issue. If your P4 does have HT, try switching it off and rebuild the map. I remember other users having problems with building with HT enabled, and there are only the two possibilities a)switch HT off or b) set the number of CPUs in the compiler window to "2" (but this will only work in some cases, better try a).
Hope that helps