title: Invalid web service call only on certain clients
body: <p>My website makes use of ajax and .Net webmethods.</p>
  
  <p>Everything works fine locally and on 99% of clients. But there are a few clients that keep getting this error: "Invalid web service call, missing value for parameter: \u0027elementid\u0027".</p>
  
  <p>The error seems to be more frequent in mornings and all clients who get this error are in the same building. I tried lots of different solutions but they generally apply when the call to the webmethod never works at all. I'm thinking the problem may be somewhere in the network of said building.</p>
  
  <p>Javascript:</p>
  
  <pre><code>    function queryDbForMeldingen() {
          //Get items from db and use the result to fill the page
          SendAjax("FindMeldingen", formatMeldingConstraints(), formatMeldingTabel);
      }
  
      function formatMeldingConstraints() {
          /*code omitted for clarity*/
          var constraints = {
              itemsonpage: parseInt(aantalItems),
              pagenr: parseInt(currentPage),
              orderby: orderby,
              orderdirection: orderdirection,
              elementid: $('#&lt;%= ddlElementen.ClientID %&gt;_ddlElementen').val(),
              filiaalid: $('#&lt;%= ddlFiliaal.ClientID %&gt;_ddlVestiging').val(),
              statusid: $('#&lt;%= ddlStatus.ClientID %&gt;_ddlEnum').val(),
              prioriteitid: $('#&lt;%= ddlPrioriteit.ClientID %&gt;_ddlPrioriteiten').val(),
              uitvoerderid: $('#&lt;%= ddlUitvoerder.ClientID %&gt;_ddlLeveranciers').val(),
              extraid: $('#&lt;%= ddlExtra.ClientID %&gt;_ddlEnum').val(),
              toonid: $('#&lt;%= ddlMeldingToon.ClientID %&gt;_ddlEnum').val(),
              datefrom: $('#&lt;%= tb_date_from.ClientID %&gt;').val(),
              dateto: $('#&lt;%= tb_date_to.ClientID %&gt;').val(),
              trefwoord: $('#&lt;%= tb_keyword.ClientID %&gt;').val()
          };
  
          return JSON.stringify(constraints);
      }
  </code></pre>
  
  <p>C#:</p>
  
  <pre><code>[WebMethod]
  public List&lt;Melding&gt; FindMeldingen(int itemsonpage, int pagenr, string orderby, string orderdirection,
      int elementid, int filiaalid, int statusid, int prioriteitid, int uitvoerderid, int extraid,
      int toonid, string datefrom, string dateto, string trefwoord)
  </code></pre>
  
  <p>I am probably being silly and missing something very simple.</p>
  
  <p>Thanks in advance,</p>
  
  <p>Blight</p>