Hi jim84x.
Thank you for using the forum.
I recommend first checking the knowledge base for this product at this link:
http://www.support.xerox.com/support/phaser-8400/support-options/enus.html
Select Troubleshoot and then in the search field located on the right enter your search words such as '2 sided'.
There are a few solutions that might help you.
If not, you may want to contact support at 1-800-835-6100 or by using this form 'FastTrack to the Expert'.
While sending a two page printout from a website to my 8400-B, it printed the first page and then seemed to lock up and posted this message: 'Adjust tray 2 size press i'. My 3 yr old computer has the same software, etc. This had happened about 6-12 months ago, and after opening and shutting the Tray 2 several times, or switching to sheet feed for some pages, then it corrected itself. Not this time.
It did make some re-start noises and had to 'warm up' from 15%.
It will send a blank sheet through after opening/closing Tray 2, or sometimes prints the 4th page of the Cleaning Page with the solid checkerboard of colors. While opening the Tray 2 the screen will also say, 'cleaning sheet needed'.
Overall page count is low @ roughly 28,000. Shut the printer off three times -- no change. Shut down the computer once, and no change. Any advice is appreciated! Jim