Loosing Attributes in DropDownList asp.net - asp.net

Question

I set attributes into a dropdownlist
the problem is that when I try to read them in a button click I get null !!
I am not sure of this is something to do with the postback or not but you will see my code below
Why is that and how to fix it?
This is my Code
protected void ddlReps_DataBound(object sender, EventArgs e)
{
foreach (System.Data.DataRow row in dt.Rows)
{
ddlReps.Items.FindByValue(row["ReportID"].ToString()).Attributes.Add("ReportPath", row["ReportPath"].ToString());
ddlReps.Items.FindByValue(row["ReportID"].ToString()).Attributes.Add("ReportServer", row["ReportServer"].ToString());
}
string AttribValue1 = ddlReps.SelectedItem.Attributes["ReportPath"];
//When I check here I can see the valu
}
protected void btnViewReport_Click(object sender, EventArgs e)
{
string AttribValue2 = ddlReps.SelectedItem.Attributes["ReportPath"];
//Here is null :(
}
ALso here is the page load code
protected void Page_Load(object sender, EventArgs e)
{
if (!User.Identity.IsAuthenticated) // if the user is already logged in
{
Response.Redirect("~/AccessDenied.aspx");
}
if (!Page.IsPostBack)
{
if (Session["USERNAME"] != null)
{
lblWelcome.Text = "Welcome back " + Session["USERNAME"].ToString();
}
string connStr = ConfigurationManager.ConnectionStrings["Main"].ConnectionString;
SqlConnection conn = new SqlConnection(connStr);
try
{
conn.Open();
SqlCommand cmd = new SqlCommand("mySP", conn);
SqlDataAdapter da = new SqlDataAdapter(cmd);
cmd.CommandType = CommandType.StoredProcedure;
da.Fill(dt);
if (dt.Rows.Count > 0)
{
//Populate your DropDownList
ddlReps.DataSource = dt;
ddlReps.DataTextField = "ReportName";
ddlReps.DataValueField = "ReportID";
ddlReps.DataBind();
}
}
catch (System.Data.SqlClient.SqlException ex)
{
string msg = "Fetch Error:";
msg += ex.Message;
throw new Exception(msg);
}
finally
{
conn.Close();
}
}
and here is the markeup for the ddl
the asp:ScriptManager is used because i am using ReportViewer
<div>
<form id="form2" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<div class="report-module">
<h2>Choose your report</h2>
<asp:DropDownList ID="ddlReps" runat="server" OnDataBound="ddlReps_DataBound" CssClass="ddl" ViewStateMode="Enabled"></asp:DropDownList>
</div>
<rsweb:ReportViewer ID="reportViewer" runat="server" Width="100%" ProcessingMode="Remote" Font-Names="sans-serif" Font-Size="8pt" WaitMessageFont-Names="Verdana" WaitMessageFont-Size="14pt" Height="457px" BackColor="White" Visible="False" SplitterBackColor="51, 181, 229">
</rsweb:ReportViewer>
</form>
</div>