This is a RXP installer window that prompts before anything is installed (just after the summary screen that shows the selected components, P3D location, etc.
Title bar is "Setup - REalityXP Garmin GTN (FltSIm)
Preparing to Install
Setup is preparing to install...
Then the message
(Red X) "The installation/removal of a previous program was not completed. You will need to restart your computer to complete that installation"
I'm trying to install into P3D v5, but I've also tried with v4 and I get the same error.