I have the same error. I was following the tutorial “Become a Rapid Developer” and just finished 4.3.
Might I suggest you take a look at your domain model, discover if there are any indexes present? You can see that here:
If so, take them out for the moment, and see if that solves the problem.
If that doesn't help, I'd try to clear the deployment directory: hypothetically, if you've made changes to your model when data is already present, then that change could trigger this error. Cleaning your deployment directory works like this:
Hope this helps; if it did, please mark as the correct answer ;-)