Hello if you click on the CTRL+T you will open the Table Viewer window, there you will see a dotted line for the loop where you see the error message. Just check the fields the line is linked to and rename anyone of the fields to anything else and then reload to get rid of this issue. QV automatically detects the tables and columns with the same name and tries to make an association, however we need to clear some by dropping them.
Eg: you might have a customer ID and Customer Name in Customer table and Customer ID, Customer name in sales Table, then you have to change the Customer in sales to something like Sales Customer so that it links with the Customer ID. Hope this helps.