|For me, it looks like there is an old printjob in the printqueue of some of your PCs or maybe a print server, if you have one.|
User-Agent:Mozilla/4.0(compatible;MSIE 7.0;Windows NT 6.1;Trident/5.0;
The line tells me, that it must be a Windows PC running Mozilla web browser.
You have to check the print queue of that printer on all the PCs in your environment, and delete old but still running print jobs.
In most cases, it sounds easier as it is.
Often you can try deleting the print job, but it doesn't work.
Therefore, you first have to open the printers printqueue, mark the printjob, stop the printqueue service in the Microsoft services, delete the printjob and restart the printqueue service.