I found out that some special marks can't be used in aircraft.cfg for titles, etc.
PMDG's Operations Center doesn't like them and they might generate some errors like informing you about missing livery on the list, even if entry is already there. In case of LN-KKM, quotation marks were the problem.
I removed them and re-uploaded fixed .ptp file so if you already installed this repaint, please remove it via OP Center and check in (...\Airplanes\PMDG 737-700NGX WL/) path for any remained files of this livery. If there is nothing left, you can download the fixed version (link down below) and install it again. No issues should occur this time, I checked it twice.
Fixed File (.ptp)