If you chose a server hostname that can't be resolved by the license server, a message like the following will appear in the license server debug log file:
16:52:11 (lmgrd) "<your_hostname>": Not a valid server hostname, exiting.
16:52:11 (lmgrd) Valid license server system hosts are: "put_server_name_here"
16:52:11 (lmgrd) Using license file "C:\license_files\license.dat"
You may have chosen a hostname that resolves but is not the actual hostname of the license server. In that case, the license server will start without errors but your clients will fail to get a license. The errors on the client will most likely not indicate a server hostname problem so be sure to get the correct name for your license server.
It's helpful to run 'ipconfig /all' on Windows and the 'hostname' command on Unix/Linux to verify the server's hostname. It's also a good idea to 'nslookup <hostname>' to verify that the IP address that is returned is what you expect. Often, the hostname resolution differs between the network lookup and the local host lookup.