I had the same problem as original poster RichB and, like Georgetastic, solved it by changing the order of my table joins. I had a complex query with 9 tables, all of which used left joins. In the query Builder I clicked the "Join Tables" button to open the Tables and Joins window. I moved the tables around on the screen to get a visualization of how the tables were joined. In my case I had one monthly data table at the center of the visualization. The other tables were lookup tables that provided descriptions for the data values in the monthly data table. (I needed left joins because the monthly data table might have new values not found in the lookup tables). By first joining the monthly data tables to the lookup tables and THEN joining the lookup tables to secondary lookup tables, all the errors went away. Hope this helps!
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