Can't set data value for node that has children!

1. What is the problem? Be very detailed.
ONA website does not accept the uploading of ODK form. The error message is:

"DK Validate Errors: >> Something broke the parser. See below for a hint. Can't set data value for node that has children! The following files failed validation: ${tmpgste5kx2} Result: Invalid
Your file should have the .xls or .xlsx file extension because Ona uses XLS Forms to create forms."

2. What app or server are you using and on what device and operating system? Include version numbers.
I am using ODK Collect v1.28.2
I am trying to upload to https://ona.io/

3. What you have you tried to fix the problem?
Reviewed form

4. What steps can we take to reproduce the problem?
I am happy to share a copy of the form.

5. Anything else we should know or have? If you have a test form or screenshots or logs, attach below.GB8_Coop_Capacity_Assessment_Oct2020_DRAFT.xlsx (225.9 KB)

Issues with Ona's website are best addressed by Ona. Have you tried contacting them at https://ona.io/contact.html?

Thank you yanokwa - will do so now.

ONA support responded within a few hours with the following "After going through the form, we were able to establish the cause of the error. Apparently you have a relevant condition in the default column.
This is on row number 38. I have updated this by moving it to the relevant column."
Thank you.