Further to the various posts concerning the disappearing ON printer, I have
been able to solve the problem on my computer by identifying a conflict
resulting from a later program that installed a pdf printer. I used the
following procedure:
1. Go to Controp Panel - Printers
2. Identify the printer (in this case pdf printer) installed after ON.
3. Right click mouse and open properties.
4. Go to Ports tab and check entries.
5. Check if the box next to "Send to Microsoft OneNote Port:" is ticked.
6. If ticked this appears to be the source of the conflict.
7. Delete the offending printer driver.
8. Perform a repair install of ON.

In my case this solved the problem. Hope this is helpful for others.

Donato