Nitro Pro 11: limited validity?

[gretha.dewit@gmail.com]

In October 2017 I bought Nitro Pro 11, but I can't use it anymore. I get messages my account is expired. But I think there's no limited validity?
I've tried to reinstall, but that isn't possible, than I get the message "Once you click “Deactivate”, you can activate your license immediately by entering the below serial number into Nitro Pro."

But when I fill in the serial no. it says: "Sorry. You may only deactivate 0 devices."
How can I activate my Nitro Pro 11 again?

Meanwhile, because I need to use Nitro, I have downloaded a free trial of Nitro Pro 12, but I don't want to pay for that after the trial, because I payed allready for Nitro Pro 11.

[Allain Umailin]

Hello @gretha.dewit@gmail.com,

Thank you for reaching out to us through our Community Forums!

To reinstall your Nitro Pro 11, kindly uninstall first Nitro Pro 12 by going to Control Panel > Programs > Programs and Features then reboot your machine.

After rebooting, please go this page and download the correct installer: https://kb.gonitro.com/knowledgebase#/search/online/000004464

If you are not sure which to pick, this will help: https://kb.gonitro.com/knowledgebase/#/search/64/000003790 

After installation, you can activate by opening Nitro Pro, clicking on the Help tab > About Nitro Pro > Activate and entering your Nitro Pro 11 serial number.

Should you have further questions, please do not hesitate to reach-out again.

[gretha.dewit@gmail.com]

Thank you for your help @AllainU, it worked!