XML schema

[ggirf14]

I'm trying to edit an XML file with Excel 2013 (Office Pro)
The source have the following 2 lines at the top:
<!--?xml version="1.0" encoding="utf-8"?-->
<arrayofsessiondata xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">

I cannot find a way to save as XML with excel and get the same two first lines I get the following:
<!--?xml version="1.0" encoding="UTF-8" standalone="yes"?-->
<arrayofsessiondata>

Problem is an error message from the application that needs to use the edited file from Excel.

System.InvalidOperationException: There is an error in XML document (10, 176). ---> System.FormatException: Input string was not in a correct format.
at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatinfo info, Boolean parseDecimal)

1- I started by importing the schema using Developer / XML Import
2- I tried to replace the two first lines to match the original document with no luck.


Question: How can I edit an XML file without changing the format or schema?

Leaving for the weekend ... hoping to read feedback Monday.

Thank you
Gilles.</arrayofsessiondata></arrayofsessiondata>