Hello,
In most circumstances you should not need to register LabVIEW for each user on the machine. However, something bizarre might have happened in your situation. If when you start LabVIEW, it does not prompted you to enter in the serial number, I would look at this
article for alternative methods to register LabVIEW. Also, even though you entered in serial number on the license server, you still need to enter the serial number on the client machine as well. I hope that this information helps you out.
Regards,
Kevin L.
Applications Engineer
National Instruments