FileUpload.HasFile give always false
<p>this is my code where my FileUpload control is outside of update panel but when I click on save button which is under update panel give fileUploadAttachment.HasFile = false</p>

<p>ASPX </p>

<pre><code>&lt;asp:Literal runat="server" ID="lblAttachment" Text="Attachment:" /&gt;&lt;asp:FileUpload
            ID="fileUploadAttachment" runat="server" Width="488px" /&gt;
        &lt;asp:UpdatePanel ID="updatePanelAction" runat="server" UpdateMode="Always"&gt;
            &lt;ContentTemplate&gt;
                &lt;asp:Button ID="btnSave" runat="server" Text="Save" OnClick="btnSave_Click" ValidationGroup="Save" /&gt;
                &lt;asp:Button ID="btnTest" runat="server" Text="Test" Enabled="false" OnClick="btnTest_Click" /&gt;
                &lt;asp:Button ID="btnConfirmTest" runat="server" Text="Confirm Test" Enabled="false"
                    OnClick="btnConfirmTest_Click" /&gt;
                &lt;asp:Button ID="btnSend" runat="server" Text="Send" Enabled="false" OnClick="btnSend_Click" /&gt;
            &lt;/ContentTemplate&gt;

        &lt;/asp:UpdatePanel&gt;
</code></pre>

<p>CS</p>

<pre><code>protected void btnSave_Click(object sender, EventArgs e)
{
    CampaignBAL campaignBAL;
    string tmpFileName = "";
    User user;
    Campaign campaignDetail = new Campaign();
    int? campaignID;

    if (fileUploadAttachment.HasFile) // return always false
    {
        tmpFileName = string.Format("{0}\\{1}{2}", Server.MapPath("TempUpload"), Guid.NewGuid(), Path.GetExtension(fileUploadAttachment.PostedFile.FileName));
        fileUploadAttachment.PostedFile.SaveAs(tmpFileName);
    }
}
</code></pre>

<p>please help me how can I fix it</p>
