HP LaserJet M5025 Multifunction Printer series - Manual (Page 209)

Clear jams from the optional duplexer
The control-panel message 13.XX.YY Jam inside duplexer alerts you to a jam in the optional duplexer.
To clear the jam, follow the instructions on the onscreen dialog box or follow the steps below.
1. Remove the duplexer.
2. Remove any media from the duplexer.
3. Reinstall the duplexer.
ENWW Clear jams 197