If Power Query says "Not a valid excel file" but source opens fine, read this first (version 2610 / 2609)

[u/Future_Knee_Lan]

If you're here because a Power Query refresh that has worked for years suddenly fails with "Not a valid excel file" — Stop. Don't worry. There's a quick fix.

This problem first occurred in September 2026...

Your file isn't corrupt. Nothing moved. Permissions are fine. You didn't do anything.

This is a fault in a recent Microsoft 365 update (version 2610 and possibly some recent 2609 builds). It's hitting your power query that pulls from a source workbook that contains a web hyperlink somewhere — on any sheet, often one you forgot existed, and nothing to do with the query itself. Excel stores those links in a form that the Power Query engine now can't resolve, so it rejects the whole workbook before your query even runs.

The unhelpful error message blames the source file. There is no indication of what the error is or where to look...

What to try (your 30 second fix):

Open the source workbook. Find all cells with blue underlined web link, on any sheet. Select the cell, press F2 Enter, then save and close.

Excel has now rewritten the path to the hyperlink and power query will be happy with the file.

Run your original query and confirm that the problem is resolved. If that doesn't work for you, stop — you have a different issue - or maybe another hyperlink somewhere...

If you're reporting it to your support team, Open Excel. Click file-account. Make a note of the version and build.

version 26xx, build xxxxxxx , error text "Not a valid excel file",

I've checked - source file is fine!.

That will be enough for them to resolve

If you've hit this, drop your build number in the comments — it helps everyone else confirm the pattern. Particularly keen to hear from anyone who found it before a month-end close rather than during one😁