Add Table greyed out in Table Builder (Essentials)

Trying to build a simple report using table builder.
Reporting on G/L Entry table, linking to the Cust. Ledger Entry and then to the customer and salesperson tables. The problem is that I can only link one table to the cust. ledger entry table - the 'Add Table' button is greyed out once I link to one table. See screen print attached.

• Add table JET issue.gif