There's three ways to approach the problem you are having. First, I am assuming that this is a dedicated printer connected via parallel cable and not a network printer.
If that is the case you should investigate your cable first. HP printers are bi-directional. They keep an open conversation with the machine printing to them. If the cable is a one way cable the printer may be telling the server that it needs to hold to add paper, but the server doesn't get the message so it just keeps dumping the job. If this is the case you can prove the point by looking at your print queue before you add paper the next time. If the job is still there this is not true. If the job is gone this is a possibility. Unfortunately you can't tell what type of cable you have by looking at it, but you can go to Office Max, Staples, Circuit City, etc. to get a bi-directional print cable.
If the job is gone you may have a different problem. Make sure you have a bi-directional cable first and if the job still disappears before you add the paper then your problem is the printer. The job may have been sent to the printer. The printer will accept as many pages of a job as it can hold in memory. If the printer receives the entire job it should keep what isn't printed in its memory until the paper is added. Try a different printer on this server if you can.
Finally, if the job is still in the print queue that is easy. Add the paper and resume printing. Use lp -H to resume printing. Bring up a man page on lp to get the exact syntax for your OS version.
Hope this helps,
Charles
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