Formula.Firewall: Query references other queries, so it may not directly access a data source.

The error can occur from privacy permissions as well. It may be necessary to take the steps outlined in the solution above and also to change the privacy options.  File>Options and settings>Query Options>Privacy

Then choose "Always ignore privacy level settings".

Hi MattAllington, thanks for the info.. 

Yes I was able to get around it just now by effectively moving all of the steps from the other query into the same query. This gets around the problem but it's a bit annoying.

First of all, this link mentioned no longer exist, so this is definitely not a solution.

Then. In my scenario, I've defined a transformation for a JSON file from a known format as a formula. This transformation DOES use data from other sources, because it's exactly what makes it useful as a formula, and the very reason for it to be converted into a formula.

Problem is, this formula becomes useless due to this error - unless I go and apply the security settings fix.

I understand this won't work in the cloud. But then, how to fix it AND keep the formula useful?

MattAllington Thank you for sharing, the Blog by Ken Puls, saved alot of my hair. (Very frustrating, but the below made sence and helped alot).

Thank you Matt. That solved the problem. 

I always know it's a good solution when I see Matt's name!

Updated URL for Ken Pul's article: https://excelguru.ca/power-query-errors-please-rebuild-this-data-combination/ 

Dead link

Updated link: Power Query Errors: Please Rebuild This Data Combination