don't bind data in each post back, do as below
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
Label_ExamName.Visible = false;
ds = new DataSet();
ds = con.dataFetch("Select ExamCode, ExamName From Exams");
DataList1.DataSource = ds;
DataList1.DataBind();
}
}
Also change your link button as below
<asp:LinkButton ID="LinkButton_ExamName" CommandName="Select" CommandArgument='<%#Eval("ExamName")%>' runat="server" BorderColor="Black" tyle="font-family: 'Bookman Old Style'; color: #000000; text-decoration: none;"><%#Eval("ExamName")%></asp:LinkButton>
then
protected void DataList1_ItemCommand(object source, DataListCommandEventArgs e)
{
if(e.CommandName ="Select")
{
var e = e.CommandArgument.ToString();
Label_ExamName.Text = e;
Label_ExamName.Visible = true;
}
}