Thanks for the update.
It seems you may need more information about the error.
The permissions per user role are correct.
The error message does matter. Because the page is not rendering properly on the website and so it is not possible to purchase a product if this theme is used.
I did request in advance of purchasing if there are any conflicts and was told there are not so I decided to go to the expense of trying this one out. Sadly it seems as if there is a conflict which is a show stopper because all of my products have to be customized before they can be purchased.
If the customize button is missing and so is the add to cart button and quantity buttons this means we have a non starter.
WP debug mode was already disabled.
So I'm afraid the error message does mean something in terms of this theme.
Any suggestions ?