Tiger M:
More likely it's a case of two writers using the same very common premise, one far more effectively than the other. It is possible for different writers to come up with the same idea or for a writer to be unconsciously influenced by others.
Alas, 'tis true. Long ago - about five years, maybe more - I had what I *think* was an original idea for a scenario. Certainly,I'd never heard of anyone else doing it. It's only recently that I've worked out what the story in that scenario would be, but I've never gotten around to writing it. And a couple of months ago, I read a book review in SFX of a novel which was based on a very similar concept. It's close enough that I won't be able to write my story now, because the natural assumption would be that I was ripping the idea from that novel.
Mind you, one way out is to research the field more thoroughly, and find several other examples of story that use variations on my "original" idea, and thus prove that it's already an established scenario.
My (still incomplete) story, and the story within that novel, are almost certain to be completely different, btw.
steve