Just Set your paging to false while fetching data from GridView.. after fetching data again set it to true
e.g.
GridName.AllowPaging=false;
in your case,
GridCustomColumn.AllowPaging = false;
foreach (GridViewRow row in GridCustomColumn.Rows)
{
string report_id = lblreportid.Text;
string columnname = (row.FindControl("lblcolumn") as Label).Text;
string columntext = (row.FindControl("txttextcol") as TextBox).Text;
string columnsize = (row.FindControl("txtsize") as TextBox).Text;
string sql = "delete " +
" from report_column where report_id='" + report_id + "' and column_name='" + columnname + "'";
sql1 = "insert into report_column " +
"values('" + report_id + "', '" + columnname + "', '" + columntext + "','" + columnsize + "');"+
"select * from report_column";
lblmsg.Text += "berhasil untuk tambah report column !!";
mda.execSQL(sql + sql1, connStr);
}
}
GridCustomColumn.AllowPaging = true;