Publish-NAVApp UnhandledErrorMessage

I have just upgraded a client database from NAV2009 to NAV2017. I am now trying to add in the Sales & Inventory Forecast extension, but when I try to publish the app using the Publish-NAVApp cmdlet, I get the error "An item with the same key has already been added"

There are no extensions installed in the database.

Any suggestions where I should be looking to resolve this?