Rekey failing with "Cannot open /dev/null for writing.: iostream error"

I am attempting to rekey my device with a valid zip package and valid password (confirmed both on another device) and I get the following error when I try it on my new device:

Cannot open /dev/null for writing.: iostream error

Device is a Roku Express 4K+

I have tried a factory reset on the device to no avail.

Thanks

Barry