Hi! Thanks for posting in the Canon Community Forum. I see that your PIXMA PRO-1 is experiencing an 1851 error.
I see that you have checked the inner cover and made sure it is closed. If you want to make sure that you are looking at the correct cover, please look at step 2 in the following page of the online manual:
That illustration shows the inner cover being opened. If you have not done so, I recommend opening the inner cover to make sure there aren’t any obstructions (paper or loose object) keeping the cover from fully closing. If you don’t see any obstructions on the sides of the cover, check if there are any pieces that may have broken or become loose.
The following section of the manual will show you how to use the lamps on the printer to determine the error that is occurring:
If you cannot tell what may be making the error come back, the printer will need service. We do not have service options for this printer. You can check if there are any local printer repair shops or electronic repair shops that can help.
You are eligible for a discount with Canon's Upgrade Program. This option allows you a one-time opportunity to purchase a new or refurbished product that uses Canon’s newest technologies, including such features as built-in WiFi, Airprint and Cloud Print, carries a one year limited manufacturer’s warranty, and to help you get up and running quickly, we also offer free ground shipping.
If you would like to take advantage of this option, please call our Sales Department at (866) 443-8002 from 9:00 A.M. to 9:00 P.M. (Eastern Time), Monday through Saturday. Let them know you were getting support on the Community website and the Canon Upgrade Program was offered.
I hope this information helps. Thanks again.