> Yes, I have struck this issue, my solution was to create a view of

the 4 or

> so which do work, and make the final join with the view.
> Not sure what caused it but the view solution worked for me

Thanks for the idea.
I just tried to create 5 views with the single select statements.
Then I tried to do the union with the views but I get the same error.
If I only try to union any of the 4 views it works but not with all 5
views.