I can't get the two to work together and just now wrote to AirParrot Support to see if they know about this. I have paid, current versions of both products.
I've have RemoteHD helper installed on 1st Gen ATV for years where it works great with the RemoteHD iOS app. Even better, my iPhone 4S lists the 1st Gen ATV among available devices on our home network AND it streams video to it beautifully. Frankly, RemoteHD is worth the money just for its ATV helper app that enables AirPlay support on the 1st ATV; we use AirPlay on the 1st Gen ATV way more than RemoteHD itself. We've also had AirParrot installed almost from the beginning, it works great with our 2nd Gen ATV and we love it, too. They have outstanding support.
Oddly, after years with these products we never tried to stream to the 1st Gen ATV until today.
Although AirParrot works flawlessly with my 2007 MacBook Pro core 2 duo running Mountain Lion to mirror or extend my desktop onto the TV using AirParrot to our 2nd Gen ATV, when selecting the 1st Gen ATV from among the Devices listed in the AirParrot menu on the MacBook Pro, AirParrot displays the follow message in the menu bar on the Mac, "Connection blocked."
🙁 So, no AirPlay (at least not yet) from the Mac to the 1st Gen ATV, even though it works great coming from the iPhone and the old ATV displays among other devices in our AirParrot's Device list.