From the REG: "Any cannot be prevented ability inherently cannot be prevented, which means it can never be targeted by any prevent ability. An ability targeted by a cannot be prevented ability cannot be targeted by any prevent ability. However, a cannot be prevented ability can be interrupted. Once interrupted, it can then be prevented."
Untangling that mess of wording... something that "interrupts and prevents" - just as something that "negates" - can stop an ability that cannot be prevented.
