Keith,
The license download link begins to download your license file (Mach1Lic.dat) automatically. That link can be used twice before that error message is displayed. Check your downloads folder for the license file. If it was not able to download successfully during those two attempts, you will need a new link. Log in to your account at machsupport.com and go to 'Manage My Licenses' then click 'Resend.' If you have antivirus or similar software monitoring your emails, I would advise copying and pasting the link into your web browser rather than clicking it in your email. Some customers have had their AV software eat up both download attempts without allowing the download to go through, just by "scanning" it.
Once you have your license file, move it to your Mach3 folder in your C: Drive to install. The video linked below goes over the download and installation process as well, if you prefer a visual guide.
https://youtu.be/POWYiMokRpgBest wishes,
Bryanna