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line 30 is the location in the scripts that it errored on. in this case, it's usually not that line specifically but something that eventually calls that line had was nil, which means you are probably missing an image line Alan Flygon said.
Try renaming your project to something other than Pokemon Essentials, or deleting your save file from C:\Users\YOUR USERNAME\Saved Games\YOUR GAME NAME. It could be that you do have all sprites related to your game, but it's clashing with a different project that has the same name. Two projects with the same name will use the same save folder, and thus the same save file.