Hello.
The file is created by FSrealWX itself and is not deleted with uninstall.
This file does not cause any problems either. If you want to delete the file, you can find it in this directory.
Just delete everything with fsrealwx. *
D:\Lockheed Martin\Prepar3D v4\Weather\themes\
If you find an error, then please give me exactly about your system. Which sim (FSX / P3D / Xplane). Which connection (FSUIPC / SimConnect / FSrealWX-Bridge). Which OS.