Doc/Chakotay says the aliens won't let them pass because their warp drive is damaging subspace (I think that was the line). Canonically, I don't think its ever been mentioned that Starfleet ever found a way to fix that effect they found back in TNG (I forget the episode name). If they had, don't you think Chakotay would have said something like "What do you mean they damage subspace? We fixed that!"

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"The Long Kiss Goodnight begins, more or less, with Geena Davis being kicked in the head by a deer. This was the high point of the film."

Mark

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"Why build one, when you can have two at twice the price?"

- Carl Sagan, "Contact"