It happens with some tables. When I try to use one of the zzzz tables it works. For the tables built by me, in my tests it works in one of them and does not work in two tables created by me.
I was following that YouTube video that teaches to build a financial application in nuBuilder. I was using the SQL builder on product table to join with customer in order to show the customer name on customer column (instead of his id). In this moment, when I tried to show the tables (choose on dropdown field) it happened. With both customer and product tables.
nuBuilder Forte loads the database schema at login (otherwise the system would slow down).
If you change something in phpmyadmin you'll need to login again.