SBS 2003 product key not valid

I had an old sbs 2003 sever with a failed hard drive sitting in the closet.  I put in a new hard drive and re installed sbs 2003.  I have the original disks and the OEM Microsoft License code and certificate of authenticity.  When i get the the screen where i enter the product key i get the error "product ID you entered is not valid.  Yes i have double checked the Key 10 times, but it just will not work.  Does anyone have any idea as to why this would be happening.