I know I said that if previous saves were incompatible that I would continue on with version 18.1. I attempted to run the 20.1 version as a brand new game and it did not throw an error, meaning the issue comes when it tries to load the save.
When attempting to load my save, it threw an error after compiling and proceeded to delete my save file. I knew this would be a bit risky, as Pokemon This Gym of Mine runs on Pokemon Essentials v18.1.
To recap, I have been attempting to update this game to Pokemon Essentials v20.1. As for the information relating to v5.0.0, I have run into a major snag in development.