Flying Trucker,,,, 
 Jetranger here,, I happened to have 23 of those D-18's in my huge aircraft collection, of 4,945 Aircraft in my FSX,,,  
Many of those D-18's I had to manually make work, for I made all mine Float Sea Planes by swapping some texture files,,,  
theres a trick to doing it tho,, the Trick is in the FILE name of the Aircraft Texture itself,,,  
I will download the package you have,,, and find the problem,,, for you.  
are you trying to Inject the download as it is  - - or - - add those 3 US Navy paints to an excisting D-18 in your sim 
 
  I kinda need to know that , that'll help me a lot find the cure, it can be done, I can make it work, by changing the file name of the texture files.  
I had to do it to like 13 D-18's to change them into Float Aircraft, some were CARGO and I changed them into Passenger D-18's with Floats.   
I also had to edit the Aircrafts CFG File as well, to make them Display properly,,  
Trickery involved here in the wording of the CFG File and Texture files .  
Get back with me, let me know Jetranger.