Hello and sorry about the error! It's certainly not fun when you can't play a game normally, so I'll try to help out! :-)
There are a couple things to try, but it's a little hard to know where to start without a screenshot. No worries for not having one, but if you know how to take one and upload it here, it would help a bit. Anyway, on to the fixes to try:
-Try verifying the Steam installation of Clone Drone (Or if you're using the itch version, try using the itch client or redownloading from the client.)
-As a last resort, you can try resetting the save data by holding "S" during Clone Drone's startup. Selecting the red reset button will wipe your save data, but it will also show you the save location beforehand so you can always make a backup.
So if neither of those things works, I may need a little more info to go off of. If you need any help taking and uploading a screenshot, let me know and I would be happy to help!