Hey! Glad you are enjoying the game. But sorry about the error :-/
That looks like a browser permission issue. I wish I understood this better to give you a good explanation. But you can try adjusting your browser's security settings to allow access to the data. I recommend using Chrome, though the game works for me on Firefox, as well (I haven't tried other browsers much). Set security to "standard protection" and make sure that sites are allowed to use java script and embedded content.
If that does not work, try this: hold down SHIFT + CONTROL when you hit ENTER on the start screen of the game. This will delete your save data. But the reset might be necessary after you have adjusted the security settings and/or moved to a different browser.
Please let us know if it works for you! If the problem persists, then we can look into a different fix. Thanks for playing!