There are two Ethernet network ports on the IX and Windows will decide which one is Default for that particular Windows installation. Windows selection of which one is "Default" can change if the drivers for the ports ever get reloaded or Windows updated.
Since our driver configurations are generally set to use the Default Ethernet port to communicate to the PLCs, it is possible that even though all the driver configuration is correct and the PLC is online and ping-able, that the driver does not work. This can be due to the IP address of the card Windows decides is "default" not being the correct one for your system configuration.
The easiest way to fix it (at least rule it out) is to swap IP addresses on the two cards and swap the Ethernet cables from one to the other.
To change which port Windows uses as the "Default", there is a detailed description of how to change the priority of Ethernet connections on the Microsoft web site. https://support.microsoft.com/en-us/kb/2526067