This could be due to a few possible problems.
First off, make sure that the PC from which you're running NTL Studio Utilities is on the same network as the iLink unit. The most common cause of this problem is that there are multiple networks present, and the unit is on one while the PC is on another.
Secondly, ensure that the unit is not configured to take a Static IP address. This can be done in a few ways. First, you can use the "assign IP" function in NTL Studio Utilities, enter the MAC address listed on the label on the underside of the unit, and click the "obtain an IP address automatically" checkbox. Failing that, as a last resort, you can perform a three-button factory reset on the unit, which will bring the unit to default status which includes being configured for DHCP. Please note this will also wipe your audio files, play schedules, play lists and connect-back schedules (connect-back IP and port will remain intact).
If that is not the case, check with the network adminstrator to ensure that there is in fact a DHCP server running, be it on a server machine or a router. If so, make sure it has not reached its maximum capacity, as some DHCP servers can be configured to only allow a certain amount of DHCP clients. Also, turn off the "bootp" protocol if possible, since it can interfere with the unit taking an IP Address.