Failed to open a connection to the device (-21345)

while other posts suggest the solution is resetting the printer system under system preferences this was not a complete working solution for me. As a second step i needed to go to my printers websetup page (usually the printers IP adress) and deactivate IPv6 completely. only after deactivating and then resetting the printer system in macOS i was able to regain access to my scanner completely.

hope this helps!

I have got my HP scanner working! Obtain you HP printer's IP address from network settings page in the printer and type this into your web browser. This opens the HP Embedded Web Server for your printer. Open the Scan tab. Load your document and press Start Scan button. Your scanner should now scan. To save the scanned image press the image preview button in the dark grey line near the bottom of the image. This will open Mac Preview and allow you to save the document to your Mac. Hope this works for you.

Now resolved the issue. Removed my HP printer from Printers & scanners. Reset the NVRAM by shutting down my mac, then turned back on again immediately holding these four keys together: Option, Command, P and R. You can release the keys after about 20 seconds. Having done that I downloaded the latest drivers for my printer from HP.com and then added my printer back to the Mac. The printer AND scanner now works as it did before.

I was able to solve this problem by adding my scanner's software to the list of allowed software connections under the Security & Privacy, Firewall, Firewall Options setting page. Once you have the Firewall Options screen open, click the plus sign and then locate your scanner's software. In my specific case, Epson Scan 2 was the application I needed to add to restore my Mac's connection to my Epson scanner. FWW, my Epson scanner is directly connected via a USB cable. This solution also worked for my wireless Canon printer/scanner as well.

Try the procedures in this Apple document: Solve printing problems on Mac - Apple Support

I have this also.

I have deleted the printer, re-added the printer, rebooted, unplugged printer multiple times. When adding the printer back not adds the printer and fax only, no scanner. The printer prints fine. The scanner is no longer visible to hp scan, preview or image capture.

I have tried all the measures in that support article. The scanner is still invisible. But thanks for trying Old Toad. When I figure it out I will post my solution. It is still a "Failed to open a connection to the device (-21345)" issue whatever that means?

I also have the same problem but with an HP Photosmart Premium printer. The scanner worked fine on 23rd October but failed to work on 24th October. The printer works fine. still trying to find a solution.

If all else fails or the other workarounds are a bit clumsy give the demo version of VueScan a try. Even though my Canon software works as does Image Capture I use VueScan exclusively as it is much more powerful than the other. You can run it in demo mode to see if it's what you might want.

THANK YOU so much DJB444! I did this with the 3 computers I have affected and all is as it was before, worked perfect! The last 2 computers I didn't download the drivers from HP, the AirPrint drivers worked fine. Thank you so much, hope your holidays are great this year! Stay safe!

I have exactly the same problem with an HP Officejet 6500A. I have tried everything and nothing work. This problem starts on October 23rd out of blue !!!!

What could I do ?

Yes it works that way but this is a lot less convenient...

I's working again and I didn't do anything. Weird !!!

As they say: don't look a gift 🎠 in the mouth.