This is just a quick post to share with others a potential solution to your network scanning issues with the Brother MFC-J6920DW printer/scanner.
I had recently bought the device because I wanted a larger format printer, along with the ability to scan and copy. It’s a very nice unit, and has so far worked well as a printer, but I ran into some issues when trying to scan across the network with it. I was constantly saying “An error occurred while communicating with the scanner. (-9923)”. This is under OS X 10.11.3 (El Capitan), just for reference.
After re-installing drivers several times, resetting and re-configuring the unit, it still failed. So I reached out to Brother’s support. Unfortunately, that was just an exercise in futility for me: “is your firewall disabled?”, “anti-virus turned off?”, “did you reset your router?”, “did you reset the unit?”. I know they need to go through the basics, but I despise how it’s always about circumventing the things that are supposed to help keep your network and computer secure.
After some back and forth, I decided it was time to install Wireshark on my machine, and it became very apparent what the issue was: the drivers for the scanner require SNMP to be enabled on the unit in order to use the scanning feature. Generally, SNMP is used for device management and I disabled it because I don’t want remote management of the device like that–especially without authentication of some sort. Well, if you want to scan, you need it enabled.
So, if you were like me and disabled SNMP support, and you want to scan across the network, you’ll need to turn it back on. I did it through the web interface to the unit by going to Network -> Protocol and making sure the check box next to SNMP was enabled, then clicking submit button at the bottom. Once I did that, everything worked fine.