you should do something like this.
DataTable dt1 = new DataTable();
dt1.Columns.Add(new DataColumn("ColName", typeof(System.String)));
dt1.Columns.Add(new DataColumn("ColId", typeof(System.String)));
.
.
.
SqlDataReader dr = cmd1.ExecuteReader();
while (dr.Read())
{
TextBoxdob.Text = dr["DateOfBirth"].ToString();
dt1.Rows.Add(new string[] { dr["ColName"].ToString(),dr["ColId"].ToString() });
}
MultiDropDown1.DataSource = dt1;
MultiDropdown1.DataTextField = "ColName";
MultiDropdown1.DataValueField = "ColId";
better post your codes.