RE: Paper jam (077-104) on Dell 2130cn printer when Duplexer installed.
I ran into this problem where the paper was jamming right at the exit with the same error code.
The debug tests mentioned were helpful.
What ended up being my problem was that when one of my kids removed a sheet of jammed paper:
There are 4 rolls at the exit held by dual springs. 1 of the rollers appeared to be inverted (which also looks normal). So I inverted the 4th roller and still had the same problem. As a last ditch effort, I inverted all 4 rollers the other way and it now works fine. So apparently when my child forced the sheet of jammed paper out, he inverted 3 of the 4 rollers.
Anyway, thought I would pass along my solution since the error directed me to this page.