Pilot2ATC works perfectly for 90% of my flight, but near the end of each flight, after ATC hands me off to the Tower at my destination airport, ATC tells me to contact Approach. On my last flight, Tower had already cleared me to land when I was instructed to contact Approach again. Most of my flights have been in Southern California, and I thought that, by coincidence, my destination airports were close to the edge between ATC areas, and that is why I was being handed off to Tower (always at 11 NM from my destination) and then being told to contact Approach again. My last flight, though, was in Texas, so it would be an astonishing coincidence if my destination was at the edge of ATC areas there too.

If you can email me ([email protected]) the log file for one of the flights where this happened, I can have a look.

P2A Log files are located in: C:\Users\<UserName>\AppData\Roaming\P2A_200\Logs where <UserName> is your PC user name. 
Portions of the path may be hidden by default, so be sure Windows Explorer has Show Hidden Items checked in the View tab.
A new one is created each time you start Pilot2ATC, and is closed when you shut it down. So if you take the most recent one after you have the error and after you shut down P2A, you should have the correct one.  
Dave

Dave found the cause of my problem and told me how to fix it. When I originally set up P2A, I set my Approach Radius to the same distance as my Tower radius. So as soon as I was switched to Tower, I'd reach my Approach radius and get switched to Approach. Dave suggested I use a Tower Radius of 5 NM, an Approach Radius of 20 NM (for my plane's speed), and a Departure Radius of 10 NM. With those settings, P2A now works perfectly. A big thanks to Dave for his wonderfully quick response to my problem, and for creating such a valuable program.