I find booleans a tad temperamental. I used to think it was just me but lots of people post about them. It seems sometimes Maya just cannot locate the two things you are trying to boolean in relation to each other and both disappear. I find if you try deleting the history of the objects and / or freezing transformations and / or centring the pivot it can make the process work (bit of trial and error) as can moving the objects around slightly on the grid.