Error opening an Excel file: 'xr2' is an undefined prefix. Line 1 position nnn.

Note: this problem happens with AQT v10, but has been fixed in AQT v11.

This error can happen if you have exported to a file in non-native format, then later exported to it in native format.

The Excel file has been corrupted in a minor way; don't worry - your data is still intact!

To fix this problem:

rename the file from .xlsx to .zip
extract the contents
go to sub-directory xl and open file workbook.xml in a text editor such as Notepad
the file will have an entry such as (for example):
<workbookView xWindow="1635" yWindow="1515" windowWidth="22755" windowHeight="13365" xr2:uid="{546DA524-9A7D-421C-A063-6E7ECA112F10}" activeTab="1" />
Remove the xr2:uid clause. After this, it will look like:
<workbookView xWindow="1635" yWindow="1515" windowWidth="22755" windowHeight="13365" activeTab="1" />
Save the file
Zip your files back to a .zip file. Ensure the xl directory etc are at the top level in the zip file.
Rename your file back to .xlsx

Advanced Query Tool