how to make file upload works properly

Question

I am using file upload with post back trigger  but when I attach file first time it is not accept unless attached again in the second time. In addition, without post back trigger it woks but uploading the whole page that why I tried to use trigger because without it the upload button stopped 

 

Please help

 protected void Upload(object sender, EventArgs e)
    {
        if (FileUpload1.HasFile && ddlSelect.Text == "Document")
        {
             Code for  Uploading  file code
.
.
.
}
 else
        if (FileUpload2.HasFile && ddlSelect.Text == "Video")
        {
                    Code for Uploading video file
.
.
.
}
else
       // {
                                      // for both
            if(FileUpload1.HasFile && FileUpload2.HasFile && ddlSelect.Text == "Both")
.
.
.
.

 {


}

asp code for trigger

</ContentTemplate>
                  <Triggers>
              <asp:PostBackTrigger ControlID="btnUpload" />
          </Triggers>
     </asp:UpdatePanel>