This tip suggests a useful method of resetting folders and accounts in your Notes application. It's generally useful if you have notes in iCloud and your Mac either duplicates the iCloud account or shows extraneous accounts. I've used this and it's helped several others with similar issues (e.g., cannot create new Notes folders).
- Click on mac HD/ library /caches. drag all the contents in the folder to the trash
- Click on the finder click go, hold the option key and click on libraries (will not appear if you don't hold the option key). go to the caches folder again and again drag everything in the folder to the trash.
- Go to your Finder "Go" menu hold the option key to choose "Library". Then go to Containers folder and find and delete com.apple.Notes/Container.plist
- Restart your computer.
- Empty trash.
- Try to open notes again.