migration assistant hangs snow leopard to mountain lion

We have two iMacs running Snow Leopard. Trying to replace them with new iMacs running Mountain Lion. Everything updated, sleep turned off. Both machines hang during migration assistant. One hangs showing ~28 minutes left. The other hangs showing ~1:15 left. I let them sit for hours with no progress.

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Users need to get back to work. I wish the boss would quit buying these things.

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