id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
2351	_ExcelBookSaveAs format XLSX (default workbook)	slash.cyberpunk@…		"In beta 3.3.9.2 too.
Add const:
{{{
Global Const $xlWorkbookDefault = 51
}}}

Change in _ExcelBookSaveAs function in Excel.au3:
Before:

{{{
	If $sType = ""xls"" Or $sType = ""csv"" Or $sType = ""txt"" Or $sType = ""template"" Or $sType = ""html"" Then
		If $sType = ""xls"" Then $sType = $xlNormal
		If $sType = ""csv"" Then $sType = $xlCSVMSDOS
		If $sType = ""txt"" Then $sType = $xlTextWindows
		If $sType = ""template"" Then $sType = $xlTemplate
		If $sType = ""html"" Then $sType = $xlHtml
	Else
		Return SetError(2, 0, 0)
	EndIf

}}}

After:

{{{
	If $sType = ""xls"" Or $sType = ""xlsx"" Or $sType = ""csv"" Or $sType = ""txt"" Or $sType = ""template"" Or $sType = ""html"" Then
		If $sType = ""xls"" Then $sType = $xlNormal
	    If $sType = ""xlsx"" Then $sType = $xlWorkbookDefault
		If $sType = ""csv"" Then $sType = $xlCSVMSDOS
		If $sType = ""txt"" Then $sType = $xlTextWindows
		If $sType = ""template"" Then $sType = $xlTemplate
		If $sType = ""html"" Then $sType = $xlHtml
	Else
		Return SetError(2, 0, 0)
	EndIf
}}}
"	Feature Request	closed		Standard UDFs		None	Completed	excel, xlsx