As you can read in the link below the licence manager uses the MAC addresses of a computer to create computer ID used for the activation process.
The trouble is that when you use a NI PCIe 8235 (Quad-Port GigE Vision Frame Grabber) you are adding 4 Ethernet ports to you computer and any change to any of these ports (even a fix IP change of one of the ports) will change the computer ID and therefore you will need to re-activate all your NI products... As day to day users we simply cannot work that way.
The knowledge base article below explains that in such cases we can get the hard drive serial number, send it to NI and they'll give us a computer ID based on that HDD serial instead of the computer ID given by the licence manager and we can then use it for the activation process.
The point of this idea is to ask NI to improve the licence manager so we don't have to go through this issues, I think the licence manager should inform the user about what the computer ID is based on and tell him about the options (MAC address or HDD serial) and let him choose between the 2.
I am copying the workaround posted by crossrulz in the comments to benefit users having these issues who find this idea: "Here is a work around if you want to play around in the Windows registry:
In "Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\National Instruments\License Manager" add a string value named "DiskOnly" and set it to "true". The license manager will now only use the HDD serial number."
We have two ears and one mouth so that we can listen twice as much as we speak.