Mach4, its plugins (Galil, Darwin, Moduleworks, etc.), and MillWizard use a PC ID to recognize your unique computer. This ensures that your license is only being only used by you. The PC ID is created by our software based on several components found in your computer. If one or more of those components change, the PC ID may change as well. If you have run a hefty Windows update recently and found Mach4 was no longer recognizing your license file, that is most likely the cause. The "why" in this case is less important than the next step, which is updating your license to include your new PC ID.
If you purchased your license from machsupport.com directly, you can use the license maintenance features to update or change your PC ID. To do so, log in to your account there and go to 'Manage my Licenses.' Copy the PC ID shown in the Help>About menu in Mach4 and paste it into the PC ID field below your Mach4 license. Double check that it matches what is shown in Mach4 and click 'Add.' A new license will be generated and a link to download it will be sent via email.
If you purchased your license from an authorized reseller (who did not provide you a coupon to be used at machsupport.com), you will need to contact them for a replacement license file as they are responsible for maintaining their customer license files.
Mach4 licensing: https://youtu.be/_sSofveXnkQ