Convert Milliseconds to Readable DateTime c#

[amean_n]

Hi there,
I'm trying to output into the gridview row (15) the date in dd/mm/yy or any other readable format.

I keep getting an exception.

Whta can I cahnge in the following code to fix this issue?

Many thanks.

I have to following code:

 protected void gvReport_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
          
            Int64 iEntryDate = Convert.ToInt64((string)e.Row.Cells[15].Text);
            System.DateTime dt = new System.DateTime(1970, 1, 1);
            dt = dt.AddSeconds(iEntryDate);
            string s = dt.ToLongDateString();
            e.Row.Cells[15].Text = s;


            
        }
    }