Some Macs because of how they are configured will change the
hostname (computer name) everytime their connection is changed.  

As this name change the license on the machine will become invalid
and prompt you to re-license.  The following steps should fix this.

You can use this method to "lock" your Mac's host name to a specific value:

    Launch Terminal.app, typically located on the path:

    /Applications/Utilities

    Enter the command:   sudo vi /etc/hostconfig

    Note: You will need to enter your Mac OS X administrator password before the editor opens.

    At the end of the file, add the line:  HOSTNAME=the_host_name   (here enter a name like   MY-MACBOOK-PRO)

    Save the file and exit the editor.

No go ahead and open the program.  Register if prompted to do so.  Close and open the machine to make
sure it retains the license.  Now watch over the next few days to see if this solves your problem.