I'm having the same problem.  Have tried entering the product serial in the various ways suggested on the site - upper case letters, lower case letters, not using caps lock and still nothing. I got Poser 7 when it still belonged to e-frontier and registered it with them so maybe thats what the problem is. I found a page on their site that allows you to register the product but  whether that was successful I don't know: the resulting web page just said I would be contact by support....I've email support about the serial not being accepted and now I've got to wait. Hopefully they'll get back to me before the upgrade deal ends.......