Kopernicus wasn't able to load the custom planetary system due to an exception in the loading process. Loading your saved game is NOT recommended, because the missing planets could corrupt it and delete your progress.
I am using Kopenicus 1.9.1 but the game says "Incontable Mods: Kopenicus with this version of the game." My KSP is version 1.10.1, what is the problem?