Failure to set up users on my EX2 Ultra

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I recently reformatted my device and reset to default to set up a new group of members in a walking group that use the WD cloud to swap vids and pics. For some reason every time I try to set them up I get the same message:
Failed to create device user. (400073)
My internet is working fine and I am able to access my device through my Admin password.
Any ideas

Graham (Fat Boys On Tour)