Currently QtQuick 2.0 needs to be imported first, before any submodules. It is disputable whether QtQuick 2.0 should even be needed at all if you aren't using elements from that specific import, but in a declarative language the order of imports shouldn't matter for clearly defined behaviour.

This gives a module not installed error:
import QtQuick.Particles 2.0
import QtQuick 2.0

This works:
import QtQuick 2.0
import QtQuick.Particles 2.0