If you are out of ideas, and desperate, you could try this as a last resort:
[1] go to: C:\Users\KittyNin\AppData\Roaming\calibre.
[2] copy file gui.json to another folder to back it up.
[3] edit file gui.json with Notepad or another text editor.
[4] delete any logical sections within that file that look analogous to this and have a __class__ of "bytearray":
Code:
"Plugin Updater plugin:version history dialog": {
"__class__": "bytearray",
"__value__": "AdnQywADAAAAAAPqAAABcgAABQEAAAKFAAAD6wAAAZEAAAUAAAAChAAAAAAAAAAAB4AAAAPrAAABkQAABQAAAAKE"
},
Be careful.
[5] Restart Calibre.
[6] If it will not restart, or you have even bigger problems, copy the backed-up original gui.json file back to where it came from, and restart Calibre. You will be back to where you were.
DaltonST