issue with install in acrobat XI on another machine

I have bought Acrobat Professional XI in 2014. I am trying to reinstall this on another machine but it is coming up with the following error. Serial Number The serial number xxxxxxxxxxxxxx is already in use by the maximum allowed computers. You need to deactivate another computer within 3 days to use this product. ◉ Retry activation. I have already deactivated one of my other computers. ○ Provide a different serial number.