Permissions Error on Data Refresh

I have a workbook that uses Power Query to pull in a number of different data feeds from various URLs. When I try to refresh the data I get a Privacy Level pop up, select Public, and everything works fine.

However, one of my employees also needs to be able to update this sheet regularly. A few days ago he was able to do a simple refresh and everything worked fine. Yesterday, seemingly out of the blue (No changes were made to the workbook), it says "Loading Data model" for him, but doesn't do anything else. He seems to be getting some sort of permissions error. Note that I don't get any of these errors when I refresh the file myself. Also the Privacy Level pop up no longer appears for him.

I tried to post an image, but it won't let me because I just created my account. Some of the errors read:

"Expression.Error: We cannot convert the value null to type DateTime."

"There are no connections for this query"

I assume the null is because no data is being returned, as I don't see that error when I refresh.

I hope that description is adequate, but let me know if you need any more information, and thank you in advance for your help!

The privacy pop-up is saved on a per-user basis. If he has already opened, refreshed, dealt with privacy and then saved the workbook - and no one else has done the same - then it will remember his choices. As soon as someone else opens and tries to refresh that copy, it will prompt them for privacy (even you). When you save your settings, he'll get prompted the next time as well. It's a bit stupid, but one workaround to this issue can be found here: http://www.excelguru.ca/blog/2014/10/29/tame-power-query-workbook-privacy-settings/

With regards to the question at hand, my suggestion is that he probably has different permissions to the data set than you do, or that his default date formats are different than yours. To see what is happening, you'll need to do the following:
-Open the file on his computer and edit the query that is failing
-Go back to the first step
-Click Refresh Preview
-Walk through the entire query one step at a time to see which step is kicking off the error

Once you do that, the problem may become obvious. Somewhere you have a step that is returning different results to yours. The first question is which, the second question then becomes why.