HP Designjet T1200 Printer series - Manual (Page 149)

The paper has jammed
When a paper jam occurs, you normally see the Possible paper jam message in the front-panel
display.
1. Power off the printer at the front panel and also switch it off at the rear.
2. Open the window.
3. Try to move the printhead carriage out of the way.
ENWW The paper has jammed 141
Paper issues