Same thing happened to me when helping a relative recently. Got an HDDTA from the office, wouldn't activate, swapped it for another (well worn) didn't activate. Got a tech, he said the signals were good, so he swapped the box again, at first it didn't activate, then he did something on his phone and it finally activated.
All you can do is make sure your connections are tight. Call a tech out, there should be no charge if it's faulty boxes, but there may be if it's a signal problem, with the inside wiring.