This is absolutely infuriating !Please help.
I had perfectly working models with the same M query generated date tables in them. (The date table does not refer to an external source at all !! ) On upgrading to the July 2018 release,my date table query no longer works and displays the same errors above. Power BI then asks if I would like to convert all tables from DIRECTQUERY to IMPORT, which I did. no error...but then it asks again and again and again the same thing with no effect.Turning off composite models and restarting has no effect. So like edhans I reverted to the June version, but horror of horrors the file wont open because it is now incompatible with the new version. I suspect Miscrosof delayed this latest release because of the composite models feature, well, they should have delayed it longer because it has caused a disaster for me.