And I repeat and confirm this doesn't happen here, and it doesn't happen to anyone, and the only one that had it, fixed it by doing this.
[qutoe]Is it possible to install that missing texture independently? [/quote]
You are not missing a texture, you have a file that comes with the updated Stand-Alone Addon Manager that is outdated, but installing the Stand-Alone Addon Manager will updated it for sure, unless something wrong in your system is preventing this, for example, permission problems in your FSX folder.
Check the filesize of the following file: FSX\fsdreamteam\Couatl\KLAX\__init__.pye