When I tried to reinstall I received and error message
Which one, exactly ?
By the way, it also keeps looking for "Prepar3d" which I am not familiar with. Is this a program that is required?
The Prepar3d program is a Flight sim based on FSX published by Lockheed Martin, it's not required, it's just the Addon Manager is compatible BOTH with FSX and Prepar3D.
However, it should ask you to install in Prepar3D ONLY if it finds a registry key in your system for it, pointing to its folder so, it's really shouldn't happen, if you don't have installed it.
But maybe it's related to the error message, which should have been easier to help you with, if you said *which* error was, maybe your registry entry for FSX is corrupted/wrong/missing, etc.