You will need to clear your Local Storage to fix this issue.　

For Chrome:

1. Go to Settings > Site Settings > View permissions and data stored across sites > Find "nutaku.com" and "nutaku.net"
2. Click the three dots and select "clear data" for the two items above

For Firefox:
1. Open the game, with the error message
2. Go to Tools > Web Developer > Storage Inspector
3. Open Indexed DB > pf.nutaku.com
4. Right click "/idbfs (default)" and click Delete

After that, please refresh the page and the game should load normally.