Thanks I've downloaded that. So near and yet so far.
I purchased the RA Spitfire in 2015. I have located the receipt email with the product key included.
However, when trying to install the paintkit the installer gives an error saying it can't find a valid Spitfire 2008 installation.
So I downloaded a fresh installer from the following link:
http://www.realairsimulations.net/installers/RASSpit_FSX_P3D.zip
I've installed from that and retried the paintkit. Same issue.
I have FSX SE on Windows 10 (apologies I think this might me the wrong thread) so I set up a dummy FSX MS folder in C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X so see if that would help. No joy.
Any ideas please?