upgraded to oomph today and installed new box with no problem TiVo, even though expected a V6.
anyway that installed with no problems.
but my second box worked ok but no movies etc, rebooted and now get the 7400 code and only a few channels.
tried the one I changed and same fault.
Unfortunately the 7400 error means that the box is no longer active on your account and needs to be reactivated.
Thanks Looney7, I guessed that and hoped a Virgin person could reboot for me as nightmare trying to get an answer on the phone due to centres being shut down.
Just an update, Anthony at the help centre sorted me out, new box on its way.