Hi.. when it comes to booleans you have to make sure you have a few things right they are very finickey.

make sure:

1) The edges are intersecting totaly through each other
2) The normals of both parts are going the same way (out wards)
3) Clean geometry with no 5 sided faces can cause trouble try and keep 4 sided faces.

If that dont help post the file up and I'll have a look.

Kurt