Appending Excel in Power Query Error

Hi everyone,

I have a power query that appends different files together, these files are located on a SharePoint 2010 server. Every day a new file is uploaded. The appending them worked fine in the past.

Recently my query now gives me the following error:

An error occurred in the ‘Transform File (2)’ query. DataFormat.Error: The document cannot be opened because there is an invalid part with an unexpected content type.
[Part Uri=/xl/worksheets/sheet2.xml],
[Content Type=application/xml],
[Expected Content Type=application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml].
Details:
[Binary]

This issue started occuring when the files started being automatically dropped there. The files are identical in nature, there are no data errors with it. When the file that shows an error is open and then closed, it resolves itself, no changes were made to the file. I don't know what the issue could be, have looked everywhere. I don't think it's a feasible solution to open and close the new file every day.

Edit: Added fact: I have another query doing something similar and it has no issue, the only difference between the two queries is that the source file for the one that doesn't work is automatically outputted and automatically added to SharePoint 2010 whereas the other one is manually added to SharePoint 2010. 

Any help anyone can provide would be a great help.

Thanks in advance,

Van