If you installed the Live Update that runs from inside FSX, with a Minor update message, the one that doesn't ask you to restart FSX, it's not possible it could cause to shutdown FSX, that's for sure, because it only updates files that are now known to FSX, but used internally by the Couatl.exe so, in the WORSE case, like getting a bad download for some reason, the worse it can happen, is that the Couatl program won't work properly but, being an external .EXE, it cannot affect FSX in any way.
If, instead, you got a prompt to a Major update, asking to exit from FSX, download and install the Stand-Alone Addon Manager, that *might* stop FSX from running if, due to some kind of security product, like an antivirus or a firewall, you might have ended up with a version mismatch, with some files updated and some not, because your security software has blocked some files, but let others going through.
In this case, be sure to download and install the latest Stand-Alone Addon Manager for FSX, with the antivirus DISABLED
- BEFORE launching FSX, configure the antivirus to exclude the following files from scanning:
YourFSXFolder\bglmanx.dll
YourFSXFolder\fsdreamteam\Couatl\Couatl.exe
- Now you can turn your Antivirus on, and launch FSX