The Free version was retired due to disappointing Ad revenues ($0.69 in two months!). If you got it during that time, you can continue to use it but it will no longer be available in the Market for new downloads.
The price of the Pro version will soon be lowered to make it up to you. This allows you to upgrade for minimal cost and gain all the benefits of a true Android background service. And it simplifies me having to support two versions.
I've poured many days of my life into this. I hope you think it's worth the price of a fancy latte.
Use Menu->Upgrade to go directly to the Market page.