To fix this issue, you will need to clear your Local Storage.

In Chrome:
1. Go to Options > Advanced > Content Settings > All cookies and Site Data > Find the domain "pf.nutaku.com"
2. Hit either the "X" or click "Indexed Database" > Remove

In 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.