DCT6416 Error EP01

The DCT6416 is a Motorola cable box. If I'm not mistaken, they are sold only by the manufaturer only to cable companies only to be rented to end users. There are several reasons for it, mostly cost effective. The chance of Comcast, Insight, Cox, TWC, etc. authorizing use on their systems is virtually nil in the USA. Check with the tech, but I'm pretty sure of it. Good luck with the seller.

If you didn't get it from your cable operator, it's not registered with your local headend. It doesn't matter if it was from someone with the same provider in another city. And even if they *were* in your city, when the previous customer (not owner, because the cable companies in the US don't sell them) did not return it, it was almost certainly deactivated.

For what it's worth, Google indicates the "EP01" error means "Not Connected". So either it's physically damaged/defective, or it's complaining because it can't connect to any headend infrastructure. Either way, you're not going to be able to use a box you acquired off eBay or elsewhere. On that count, Arvy is 100% correct.