Windows 98 SE installation

I am trying to install Windows 98 SE to update Windows 98 First ed. Both Widows cd’s (1st & 2nd eds) are microsoft products(no copies) but during the installation as I get to enter the product key I get the message “You cannot complete Setup withouta valid Product key”. I can get no farther in the installation and cannot decide what the problem might be. Is ther something else I might try to correct the situation. I have been using the 1st ed for many years so I am sure it is okay.