This is a 1715-AENTR, an adapter for the 1715 series Redundant I/O system.
Because it has a Redundant Ethernet interface, it works a little differently than other adapter products, though it uses the same BOOTP/DHCP and RSLinx tools to configure it.
Are you following carefully the instructions beginning on page 111 of the User Manual, Publication 1715-UM001 ?
If you are not giving the module a valid IP address, Subnet Mask, and Default Gateway then it will not accept them.
Also be sure you are not configuring the higher-MAC-ID second interface; that's done automatically, as described in the user manual.