21
HP Printer
Severity: ModerateWhat Does This Error Mean?
Error 21 means the page you are trying to print is too complex for the printer to process. The document has too many graphics, fonts, or details for the printer's processor to handle. Simplifying the document or changing print settings usually fixes this immediately.
Affected Models
- HP LaserJet 4
- HP LaserJet 4 Plus
- HP LaserJet 5
- HP LaserJet 4050
- HP LaserJet 8100
Common Causes
- The page contains too many complex vector graphics or high-resolution images
- The document uses a very large number of different fonts on the same page
- The print resolution is set too high for the printer's processor to handle
- The printer's available memory is too low to render the full page at once
- A PDF or PostScript document uses complex transparency effects or layers
How to Fix It
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Press the Continue or Go button on the printer panel to attempt printing the page anyway.
The printer will try to print the page at reduced quality. This often produces a usable result.
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In your print driver, lower the print resolution from 1200 dpi to 600 dpi or even 300 dpi.
This is the single most effective fix for error 21. Lower resolution means less data for the printer to process.
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Enable 'Print as Image' or 'Raster' mode in your print driver settings.
This converts the page to a bitmap image on your computer before sending it. The printer then receives a much simpler job.
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If printing a PDF, open it in Adobe Reader and use File > Print > Advanced > Print as Image.
This setting is especially effective for complex PDFs with transparency effects or embedded vector graphics.
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If the document has many images, try reducing their resolution before printing. Save images at 150–200 dpi for print instead of 300+ dpi.
Most people cannot see the difference between 150 dpi and 300 dpi on a printed page.
When to Call a Professional
Error 21 is almost always fixed by adjusting print settings — no technician needed. If the error appears on every document regardless of complexity, the printer's processor or memory may need attention. A technician can diagnose hardware limitations and advise on a RAM upgrade for $30 to $80. Contact HP Support at 1-800-474-6836 for further guidance.
Frequently Asked Questions
Why does error 21 only happen with certain documents?
Different documents vary enormously in complexity. A page with a company logo, background gradient, and multiple fonts takes far more printer memory than a plain text document. Error 21 appears only when the page complexity exceeds what your printer can handle.
Will adding more RAM to the printer fix error 21?
Yes. Adding more memory is a permanent fix for errors 20 and 21. Most HP LaserJet printers accept standard DIMM memory upgrades. Check HP's website for compatible memory for your specific model.
Can error 21 damage my printer?
No. Error 21 is a processing limitation, not a hardware failure. The printer simply cannot render the page in memory and displays the error. Your printer is perfectly safe — adjust the print settings and try again.