Updating data in a web DataGrid

[cashdeskmac]

Inside the UpdateCommand method of the web DataGrid control I have been given
the following code to take the updated text in each cell and write the
changes back to an XML file:

for(int i = 1; i < 4; i++)
{
MyDataGrid.Tables[0].Rows.Find(Int32.Parse(((TextBox)e.Item.Cells
[0].Controls[0]).Text))[i] = ((TextBox)e.Item.Cells[i].Controls[0]).Text;

}

I then go on to write back to the file and DataBind.

However, the code is breaking on this line, the message being that the input
string is in the incorrect format. The first column in the DataGrid contains
a number and the next 3 are strings.

A breakdown of what this code does would be appreciated, as would an
explanation as to why it is failing.