Error on apply Power Query: Expression in partition n/a in table n/a references an unknown entity

OK - Finally got it worked out.

1. Open your old broken pbix file.
2. Turn Off 'enhanced metadata format'
3. Copy all your queries out to text files.  (Quick way is to just right click on the query name in the left side of the query editor, select "copy" then click in a text editor, I use Notepad++, and hit Ctrl+V.  The whole query will be pasted into the enditor.  In Notepad++, you can add multiple tabs for each file, which is nice.)
4. Close PBI and Start it up with a new file.
5. Check the settings again to be sure 'enhanced metadata format' is really turned off. (First time I did this, it wasn't, which caused me to have to start all over again - bummer... )
6. Save the new file with whatever name / revision number you need.
7. Open the query enditor and add blank queries as needed.  Use the advanced editor to paste from your text file into the new query.  Be sure to rename them.  Pay close attention to the creation order as some of your queries will, no doubt depend on others.  Take a screen shot of your query relationships if it helps.
8. I saved and refreshed after the "Functions" and "Connection Only" queries were created.  As these don't get loaded into the model, I felt rather safe in that all of them were not causing the problem.
9. I then saved after each dimension and transaction query were created and refreshed, just to be sure if something broke i woudl know which query was causing the issue.  I also saved several versions "...Rev1, ...Rev2, etc. so if something did break, I could go back easily to the last "unbroken" file.
10. Fix up your Calendar table.
11. Create your relaitionships.
12. Recreate all your measures.
13. Recreate all yoru visuals / reports.
14. I did not turn the 'enhanced metadata format' back on.  I figure if the model works without it, why break it!  I'll give it a few more revisions and try it again.  (on a test file!).

Hope this helps...