asp.net - Fileupload1 ID tag is not recognizable -

i know there lot of solutions in case nothing working. trying fileupload tag id in asp.net server caught in error .it works fine in 1 page when move code in page .here comes error "the name fileupload not exists in current context" have placed fileupload in bootstrap modal .

<div class="modal-content">             <div class="modal-header">                 <button type="button" class="close" data-dismiss="modal">&times;</button>                 <h4 class="modal-title " style="text-align:center">email customer</h4>             </div>             <div class="modal-body">                  <form id="form1" runat="server">                      <div class="controls controls-to">                         <label class="control-label">to:</label>                         <asp:textbox id="textboxemail" class="form-control" runat="server"></asp:textbox>                             </div>                      <div class="inbox-form-group">                         <label class="control-label">description:</label><br />                          <textarea id="textarea1" name="message" rows="12" class="inbox-editor inbox-wysihtml5 form-control" runat="server"></textarea>                      </div>                     <br />                     <div class="inbox-compose-attachment">                         <!-- fileupload-buttonbar contains buttons add/delete files , start/cancel upload -->                         <span class="btn green btn-outline fileinput-button">                            <asp:fileupload id="fileupload"  runat="server" />                         </span>                    <br />                           <br />                            <br />                           <asp:button id="button2" onclick="buttonclick" runat="server"  text="button" />                   <%-- <asp:button id="button1" runat="server"   text="send email"onclientclick="sendemail" usesubmitbehavior="false" causesvalidation="false" />--%>                  </div> 

and end code

  protected void buttonclick(object sender, eventargs e)      {             {             long id = convert.toint64(page.request.params["id"]);             var invoiceheader = dberp.invoiceheaders.where(x => x.idinvoiceheader == id).firstordefault();             if (invoiceheader == null)                 return;              fileupload file = fileupload; //error shows here             byte[] filebyte = null;             if (file.hasfile && file.postedfile != null)             {                 //to create postedfile                   httppostedfile file = fileupload.postedfile;// , here                 //create byte array file len                 filebyte = new byte[file.contentlength];                 //force control load data in array                 file.inputstream.read(filebyte, 0, file.contentlength);                 if (invoiceheader.id_common_resource != null)                 {                     common_resources oldres = dbcommon.common_resources.where(x => x.idresources == invoiceheader.id_common_resource).firstordefault();                     if (oldres != null)                          oldres.content = filebyte;                      else                     {                         common_resources res = new common_resources();                          dbcommon.common_resources.add(res);                         res.content = filebyte;                         invoiceheader.id_common_resource = res.idresources;                     }                  }                 else                 {                     common_resources res = new common_resources();                      dbcommon.common_resources.add(res);                     res.content = filebyte;                     invoiceheader.id_common_resource = res.idresources;                  }                 dbcommon.savechanges();             } 

and designer.cs

namespace webapp.portal {   public partial class invoice {      /// <summary>     /// form1 control.     /// </summary>     /// <remarks>     /// auto-generated field.     /// modify move field declaration designer file code-behind file.     /// </remarks>     protected global::system.web.ui.htmlcontrols.htmlform form1;      /// <summary>     /// textboxemail control.     /// </summary>     /// <remarks>     /// auto-generated field.     /// modify move field declaration designer file code-behind file.     /// </remarks>     protected global::system.web.ui.webcontrols.textbox textboxemail;      /// <summary>     /// textarea1 control.     /// </summary>     /// <remarks>     /// auto-generated field.     /// modify move field declaration designer file code-behind file.     /// </remarks>     protected global::system.web.ui.htmlcontrols.htmltextarea textarea1;      /// <summary>     /// fileupload control.     /// </summary>     /// <remarks>     /// auto-generated field.     /// modify move field declaration designer file code-behind file.     /// </remarks>     protected global::system.web.ui.webcontrols.fileupload fileupload;      /// <summary>     /// button2 control.     /// </summary>     /// <remarks>     /// auto-generated field.     /// modify move field declaration designer file code-behind file.     /// </remarks>     protected global::system.web.ui.webcontrols.button button2; } } 

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