Desktop Software License keys are tied to the network Mac address of the computer they are install on, so anything that may change the network Mac address of the computer may cause your license activation to become invalid.
Unfortunately, many of the latest OS versions can switch the network Mac address by switching on and off of the IPV6 and IPV4 protocols.
If you are experiencing the license key being deactivated from time to time, to prevent this from occurring, you'll need to disable the IPV6 protocol on your computer.
Instructions for Windows: http://www.informationweek.com/how-to-disable-ipv6-on-windows-7-/d/d-id/1099490
Instructions for Mac: http://osxdaily.com/2014/04/18/disable-ipv6-mac-os-x/