I have to re-install my Adobe Acrobat Standard XI and have a serial number but it is not working???

i have re-install adobe acrobat standard xi , have serial number when bought adobe not working...says serial number invalid???

invalid license http://helpx.adobe.com/creative-suite/kb/error-serial-number-valid-product.html

-and more in http://helpx.adobe.com/creative-suite/kb/invalid-serial-number-cs4.html

More discussions in Installing, Updating, & Subscribing to Acrobat

adobe