Hi mrbooks,
Have you tried associating your previous Sellathon account with your Auctiva account? This can be done at Auctiva -> My Account(tab) -> Sellathon Settings by clicking the "Get Existing Account" button.
If that doesn't do the trick, I recommend filing a supoport request using the appropriate link on our help page:
http://www.auctiva.com/free_auction_software_help/help.aspx
-Mike