Answer One: (by MrFixIt) Lots of people running into this. FlexLM looks for the MAC address on eth0 and nowhere else! Eth0 is usually the first network interface, but newer versions of Linux do things differently. If you go to the directory where the devices are mapped -- could be /etc/config or /etc/iftab or /etc/udev and rename eth1 to eth0, then it should work.
Answer Two: (by Jim Logajan) The following is probably the cause:
Flexlm goes looking for the MAC address on the Ethernet interface named "eth0" and if it doesn't find it, it returns an empty or blank hostid. Most likely your only Ethernet interface was assigned the name "eth1" rather than "eth0".
One way you may be able to rename the interface from "eth1" to "eth0" is to use the Linux "Network" Administration GUI tool (you'll need the root password). In the window that appears you would select on the "Hardware" tab to display a dialog that shows all the interfaces. Select the row with the eth1 device and click on the Edit button. In the dialog box that appears you should see a field that allows you to rename interface to eth0. Just follow through on OKing and saving as indicated. A reboot may not be needed, but probably should be done to insure the change is persistent.