Hi mikealpha,
As you are aware I have recently responded to your other question regarding the Cessna 207.
What version of X-Plane are you using? If you have updated to XP11.40b3 then you need to take into account the message found at https://forums.x-plane.org/index.php?/forums/topic/160879-thinking-of-downloading-a-x-plane-beta-version/ The same may also apply to your Cessna problem.
If you haven't updated then I would also suggest leaving Beta versions to experienced X-Plane flight simmers. I personally leave Beta versions alone and only upgrade when an official release is made.
When loading an aircraft in X-Plane from the standard listing a serial number is not required. If the serial number relates to the aircraft then that suggests to me that the piper aircraft is a 3rd party purchase. You may also need to consider the information previously supplied in the link found at https://questions.x-plane.com/26359/bought-cessna-xplane-store-load-game-pilot-blocks-cockpit-view
However, if the serial number relates to the X-Plane software then it tells me you have a digital download. After starting X-Plane and when prompted apply the password key. You need to ensure you are connected to the internet at all times when running X-Plane as the software performs a silent background test to ensure you have a legal copy. If the software cannot detect a password it will shut you down. Other flight simmers have the same problem
Would appreciate advice on your solution. Send me a private message through this forum. To send the response click on my user name and then the green box should appear along with my other details. Click the box to create the response.
Good luck.
Glenn