>O! Then you must select whole sheet or only used range to Unlock all cells and then lock only header row.

Yep, this worked:

if m.tlLockHeaderRow && we need to prevent headers from modifying
			** Code from Borislav Borissov
			loSheet.UsedRange.select
		    loExcel.Selection.Locked = .f. && First we need to UNLOCK all cells
		    loExcel.Rows(m.lnLines + m.lnOffset).Select && Select header row of the sheet
 		    loExcel.Selection.Locked = .t. && Lock Cells in first row
			loExcel.ActiveWorkbook.ActiveSheet.Protect(,.t.,,.t.)
    endif 	

And it's good I posted because I see I have wrong comments on the loExcel.Selection.Locked = .t. line.