Please refer to the given links for the error : Error "The serial number is not valid for this product" | Creative Suite
You can also check system requirements here : System requirements | Adobe Creative Suite 6
Hope it helps.
Perhaps a silly question, but you did make the purchase at Adobe.com, and not a third-party vendor?
Yes, I bought the download version at Adobe.com with credit card.
If the links which MacnTutor sent you do not clear up the issues, I suggest you contact Adobe directly,