System Extensions Cannot Be Used Error
Its possible you deleted some printer folders but left the actual kext files in place.  To delete the kext files that are causing an issue, open terminal and type

sudo rm -rf /System/Library/Extensions/Belcarra.USBLAN_netpart.kext


The system will ask for your password.

Repeat this for any other files the system complains about.  You will then need to reboot.

If something stops working as a result of the above, you may need to re-install the drivers.