Writing to excel compatible files

Hi,

My application creates a excel report in old version 97-2003 work sheet.

to run the test I need to add couple of line into it.

The new test machine has Excel 2016.

I used to open and write using ..

 var app = Sys.OleObject("Excel.Application")
 var book = app.Workbooks.Open(fname);
 var sheet = book.Sheets(sheetName);
..............
app.Visible = true;
 xlRange = app.Range('A1').Activate(); 
 app.ActiveCell.EntireRow.Insert(); //.Insert();
 for(i=1;i<18;i++){ app.Cells(1,i)= headVal[i] }
.....................
 book.Save();
 Delay(7000);
 app.Quit();

But now it doesn't work.

Opens in compatibility mode, can see writing (many lines ...) but discarded while saving.

any solutions?