Are you getting that code all the time or only when you turn on the STB? It seems to be a brief handshake issue between the STB and the TV. I get that code when I turn on my STB but goes off once the TV is on.
DUI means DVI DVI can be an issue or it doesn't have to be. there are a lot of people that have DVI pull up and it's more of a status message than it is an error message.
It is like the poster above says and references the HDMI handshake.
SO if you get dvi but can watch tv just fine then ignore the message.
IF you get dvi and can't watch tv, then it has to do with the hdmi cable and the handshake and there have been a couple work arounds for it.
so if you have that problem, you can try turning on the devices more deliberately meaning, that you turn on one box at a time, not both at the same time. if that didn't make a difference, you can try a different port on the back of your TV (that's been known to work) and or a different hdmi cable. If all else fails there hasn't been any good fixes that I have heard, outside of switching it to a component cable instead of an HDMI cable.