Acrobat XI Standard Suddenly Stopped Working

[Steve294779109bwu]

As the subject line says, Acrobat XI suddenly stopped working. So I uninstalled the product and reinstalled it (from disk). Message says that "serial number is valid by a qualifying product could not be found on this computer". Confusing, because I literally just reinstalled it. And it was working right up until yesterday. So I go to the "Customer Support Page" and a new message tells me that

The Adobe serial number you entered is invalid

It may be blocked due to misuse — or expired.

What does this mean? Who is blocking my serial number? How can a one-time-purchase software license expire? Is this all just a ruse to force me to buy a subscription?

[try67]

It means your version is an upgrade license, so you must specify a serial number of a previous full license in order to be able to use it.

[Steve294779109bwu]

Ah - that makes sense. Thank you! Too bad the disc and serial number of whatever original version I had installed years ago are MIA...  But at least I understand the issue now before succumbing to monthly payments.  Thanks again.