NIS 2010 Activation problem on 2nd PC

Hi,

 

I purchased NIS 2010 online. I installed it to my PC and activated easily. In my norton account, i can see the product key and it says there are 2 PCs remaining.

 

After couple of weeks, I installed NIS 2010 to my second PC and entered the same product key in subscription page. I receive error message "you have exceeded the number of allowable installations...." But i only installed it to 1 PC and my norton accounts shows i have 2 more PCs left. How this could happen ?

 

Please help me

Thank you