Installing serial number

I cannot install my serial number I received with purchase and download of Acrobat X! Pro. I keep getting this error message

"Serial number provided is valid but a qualifing productcould not be found on this computer"

Select a Product does not have Acrobat X! Pro listed.

I have downloaded this product and have used it for the past couple of days. It is installed on this computer. I paid a lot of money and for me not being able to install serial number creates continual

display of acrobat to buy.