Hi,
This is not right way to create data table
you shod write add column out side loop
try this it will work
private void CreateGridViewRows()
{
DataTable dt = new DataTable();
DataRow dr = null;
dt.Columns.Add(new DataColumn("RowNumber", typeof(string)));
dt.Columns.Add(new DataColumn("Col1", typeof(string)));
dt.Columns.Add(new DataColumn("Col2", typeof(string)));
dt.Columns.Add(new DataColumn("Col3", typeof(string)));
dt.Columns.Add(new DataColumn("Col4", typeof(string)));
dt.Columns.Add(new DataColumn("Col5", typeof(string)));
dt.Columns.Add(new DataColumn("Col6", typeof(string)));
dt.Columns.Add(new DataColumn("Col7", typeof(string)));
for (int i = 1; i <= (3); i++)
{
DataRow drCurrentRow = dt.NewRow();
dr = dt.NewRow();
dr["RowNumber"] = 1;
dr["Col1"] = string.Empty;
dr["Col2"] = string.Empty;
dr["Col3"] = string.Empty;
dr["Col4"] = string.Empty;
dr["Col5"] = string.Empty;
dr["Col6"] = string.Empty;
dr["Col7"] = string.Empty;
dt.Rows.Add(dr);
}