Laurence,
In either 4.0.1.0 or 4.0.1.6 if I use both InsertRows and DeleteRows the formula isn't being updated correctly. I have attached a simple example to explain the problem. If either:
sht.Cells.InsertRows(5, 10)
or
sht.Cells.DeleteRows(1, 1)
in the example is rem'd out the formula is correct. However, if both are enabled then the formula isn't being updated correctly.
In 4.0.0.1 it works as expected.
David