.NET FOLLOWER

    After migration a SharePoint 2007 application to SharePoint 2010 my jQuery scripts communicating with asmx web services stopped working. The error I got was a 500 Internal Server Error. The scripts looks as follows:

$.ajax({
  type: "POST",
  url:  "http://someserver/someapp/_layouts/Services/Products.asmx/GetProductByCountry",

  data:        JSON.stringify({ countryCode: "USA" }),
  dataType:    "json",
  contentType: 'application/json; charset=utf-8',
  context:     this,

  success: function (data) {
		     alert(data.d);
           },
  error:   function (XMLHttpRequest, textStatus, errorThrown) {
		     alert(textStatus);
           }
});

Note: The JSON object mentioned in the script is defined in the json2.js available at http://www.json.org.

This issue can be solved by adding an appropriate <webServices> section to the SharePoint application’s web.config (in my case it’s located at C:\inetpub\wwwroot\wss\VirtualDirectories\80). So, find the global <system.web> section in your web.config and make changes so that the result would look like the following:

<system.web>
  <webServices>
    <protocols>
      <add name="HttpGet" />
      <add name="HttpPost" />
    </protocols>
  </webServices>
...
</system.web>

However, from the security point of view such solution is not ideal as it allows external access through the HTTP-GET and HTTP-POST messaging protocols to all your XML web services. So, it’s better to specify the access protocols for each web service separately, not affecting other ones. The <location> element added to the root <configuration> element provides us with this capability. The sample below defines the protocols for accessing the web service reachable by the specified path:

<configuration>
...
  <location path="_layouts/Services/Products.asmx">
    <system.web>
      <webServices>
        <protocols>
          <add name="HttpGet"/>
          <add name="HttpPost"/>
        </protocols>
      </webServices>
    </system.web>
  </location>
...
</configuration>

Note that the _layouts virtual directory is available as a subfolder of every SharePoint Web site. So if you want to limit the use of the web service by only one SharePoint Web site, specify the path like someapp/_layouts/Services/Products.asmx.

PS Here is a good article about how to create a custom web service in SharePoint 2010.