Here's how I've figured out licensing works with the program IDL. You can put a newer version of the license.dat file on the users computer and it will work as long as the person has a version equal to or less than the version running on their system. The licenses are backwards compatible. When you have a licensing server that the clients connect to you need to have the same license file you put on the users computer on there. Each release of IDL comes with a new version of the flexlm license manager. If your going to use a newer version of IDL and you get your newer license then you have to install the newest flexlm license manager. The newest version of IDL aways needs the newest version of the license manager (flexlm).
So pit falls are: If you put a newer version of the license server on your license server and give it an older version of a license it will fail. If you put the newest version of the license server up with the newest version of the license and someone without the newest license (on their local machine) tries to pull a license from the server it will fail.
IDL license's for servers generate a key based on the host name of the machine and the MAC address of the primary NIC in that machine. This generated number is put in the license file. It points the machines to the license server. You can not start a license server on any other machine other than the one that has that certian host name and that certian MAC address. If you need to setup a new license server and test it before it goes live then you can give that machine the same name as the license server and spoof the MAC address so the license server will start and serve out licenses. With linux you can do this with a line like the following.
ifconfig eth0 hw ether 00:41:F3:45:BC:92 up 192.168.1.40 netmask 255.255.255.0