I was having this issue also. I found this thread and disabling Exchange Notes did the trick. Obviously, this is the solution only if you were using Exchange to begin with.
If you want to continue to use Exchange notes or perhaps try this to see if it works in general, I found a fix on this site. All works well now.
1. Delete your exchange account from the Mail, Contacts & Calendars pane in System Preferences.
2. Go to Finder, click "Go" in the menu bar, click "Go to Folder" and type in "~/Library" (without the quotes) in the box. This will take you to your user Library folder.
3. Use the search box in the finder and type in "com.apple.notes" and click "Library" in the search bar that appears. This should now find several folders and files related to the Notes app. Rename or delete everything except the help files (with the lifesaver icons on them).
4. Restart your Mac. Put your exchange account back into System Preferences, you can go ahead and activate the Notes sync service.
5. Open Notes and it should be working now!