Hi Nicolas,
There is an workaround similar that suggest in thread that you find.
Try something like this:
1. Set focus to the line that you need delete
oMatrix.Columns.Item("select an id of some cell - preference the item code").Cells.Item(line).Click();
2. Call the menuItem DeleteRow
SBO_Application.ActivateMenuItem("1293");
For save your document, you can simulate the user click in add button, like this:
SBO_Application.Forms.ActiveForm.Items.Item("1").Click();
P.S: I suggest that you insert your sales order by DI API if is possible.
Hope it helps,
Diego