I installed a new Caribbean Airlines repaint for the default 737-800 in FSX a few months ago, and it never showed up, even though I had installed everything correctly.  Anybody know how to fix this? :-?  Here's the link to the repaint I installed: http://simviation.com/1/search?submit=1&keywords=caribbean+airlines&x=0&y=0 ; :

Check if the texture directory is in the right aircraft directory. Check aircraft.cfg: are the entries correct? At the line texture, there should be a valid reference to the used texture directory (e.g. texture=carib for texture.carib)
Sometimes if nothing helps, check the aircraft with FSX Utility--Addit! Pro. You can use the test version. It shows all missing files for aircraft and should help you to fix it.

Works for me.  Two things to check..

Make sure the [flightsim.XX] from the ReadMe is edited to the correct number.  Mine, for example, is [flightsim.8]

The next, and most likely culprit is that some of the textures are 2048 x 2048 pixels (or even 4096), instead of the standard 1024 x 1024 pixels,  (I didn't have time to check them all).  The Download has a text file called "To view in high def", with the following instructions:

This is a HIGH DEFINITION texture.
In order to view in HD you will have to change a setting in the FSX cfg file.
This is quite simple:

1. Start - My Computer
2. Click on Hard Drive icon
3. Documents and Settings
4. Click on folder with Your name
5. Application Data
6. Microsoft
7. FSX
8. fsx,CFG

Scroll down to "TEXTURE_MAX_LOAD=1024 and change this to 4096.

That's it but keep an eye on this setting as sometimes it can revert back
to the Standard Definition setting of 1024.

I think your fsx.cfg can handle that if you have installed FSX SP1 and SP2. I don't think you need FSX Acceleration.

CHUCK's advice:
It will always turn back to 1024 when you make changes in sim settings.
This little neat program will make sure the TEXTURE_MAX_LOAD=xxxx  stays

tml_installer.zip