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Unfortunately, as far as I'm aware of, all the boxes provided as part of a TV subscription that allow external USB drives for storing recordings use strong encryption, in much the same way as the encryption used over the air. Just like how a DirecTV box will not work with Dish programme, the same applies with the encryption they use on external USB disks.
If you are still able to play your recordings on your original Dish Network box, one thing you can try is connecting it up to a DVD recorder to re-record the programmes you're most interested in. For copy protected recordings, you'll need a video conditioner that is capable of removing the protection. Alternatively, just store the original box and hard disk handy for when you want to play the recordings. You can pick up a new USB HDD relatively cheap for around $60 to $70 for a 500GB size.