Thank you for your question, and sorry for the inconvenience. We have deployed a fix that resolved this issue. But if this is still not working on your browser, perhaps an old version of the puzzle is being loaded for you. If so please try this:
In all browsers there are methods to "force-reload" a page without using your cache.
Windows and Linux browsers:
CTRL + F5
Apple Safari - either of these two methods:
SHIFT + Reload toolbar button
COMMAND+ OPTION + R
Chrome and Firefox for Mac:
COMMAND + SHIFT + R
After this, if you still get the same error, please send a note to email@example.com and can mark this a complete so that your child can continue with the course.