CORIOdiscover transfers the required firmware files to the CORIO3 device using the TFTP protocol. Windows Defender firewall or other firewalls may be set up to block this type of traffic. If the firmware update fails at step 3 with zero bytes transferred, it is likely that the file transfer is being blocked.
Under Allow and App Through Windows Firewall, please make sure that CORIOdiscover and CORIOdiscover.CLI is allowed in all available network types -- Public, Private, etc. Restart CORIOdiscover if it is running. In some rare instances, it may be required to restart Windows for this change to take effect. IT policy may block the ability to make changes to this setting, and the system administrator may required to make the required changes.
TFTP uses UDP port 69. This must be allowed on firewalls between the PC and CORIO3 device for the update files to be uploaded to the device.