"Your copy of Microsoft Office Professional Plus 2013 cannot be activated because the specified Product Key has already been activated the maximum number of times for your software license"
Place your version of Office in the product tag. So what is going on? Microsoft is intentionally not allowing buyers who legally bought a multi hundred dollar program activate it anymore. Microsoft has created a "activation kill" switch on all non 365 versions. It appears like me many were continuing to use their 2007-2013 versions and were happy to do so.
But Microsoft was not happy, they are losing money, their solution, an activation kill switch. Yes Microsoft is NOW STEALING copies of Office, your copy. In effect Microsoft is now stealing Office from buyers to force them to buy the 365 version. What did Microsoft do to ones who stole copies? Here is the thing, Microsoft "upgrade" it's license agreement without telling buyers then used the activation kill switch.
So what can Office Users do?
1) Abide by Microsoft and buy their latest version of Office 365, of course it's a forever monthly payment.
2) Buy Corel Wordperfect >https://www.wordperfect.com/en/< It's not like Microsoft Office and I'm used to that. Yes but at some point you did not know how to use Office and you learned. Wordperfect will open ALL DOCX and other Office files. Also WordPerfect does not have an activation kill switch. Just ensure you are connected to the Internet when Installing AND Uninstalling. It is important to be connected when uninstalling. If the current version is too much to pay then use eBay to find older versions at a reduced cost, install and use the upgrade route it is much cheaper. Just ensure you purchase a brand new older version off eBay.
3) Download and use Open Office. Open Office is 100% free and has the same features as Microsoft Office and will open DOCX files and all other Microsoft Office Files. Open Office is safe, always free and will give free updates forever. You will never get an activation kill switch or be asked to pay.
The end point is Microsoft is killing programs that buyers spent hundreds on and forcing buyers to pay monthly forever, they are about to start the same approach with Windows 10. If Microsoft is going to charge a monthly fee for Office, Windows and all their products a user will end up paying nearly $50 a month to Microsoft to turn on their own computer.
It is time to break free of Microsoft, they give enough to get users hooked then force users to pay.
Remember at some point you had to get used to how Office worked, you can adjust to another type of program.