The notice you receive gives you the specific title name in question.
The Maule has 6 default paints defined, [fltsim.0 thru 5]
In the above notice the title name in question is found in....
[fltsim.5]
title= Maule M7 260C
This is a default paint so you probably don't want to edit it. Rather, look for additional [fltsim.x] sections below [fltsim.5] that have the same title name. For example, you find....
[fltsim.6]
title= Maule M7 260C
Add some text to the name to make it unique. The added text can be anything, for example if you added a 'green' paint you could name it...
[fltsim.6]
title= Maule M7 260C green
(Note: the unique title=name requirement spans all aircraft installed, i.e. the duplicate could be in another aircraft.cfg file. This includes flyable and ai aircraft)
If you don't find any duplicate names in the default Maule's aircraft.cfg (from installing new paints) the other possibility is you have added an entire addon aircraft (another Maule) that uses the duplicate title name. You'd have to locate that aircraft and edit the title name.
Dave
At that time [1909] the chief engineer was almost always the chief test pilot as well. That had the fortunate result of eliminating poor engineering early in aviation. Igor Sikorsky
I intend to live forever....so far, so good. Steven Wright
You know....you can just rip up a to-do list.