Ajax – 500 System.ServiceModel.ServiceActivationException when making an Ajax call to WCF rest service

Ajax Call:

   $.ajax({
        type: "POST",
        url: "http://SomeService/ServiceName.svc/GetSearchResults",
        data: JSON.stringify({ parameters: serviceParameters }),
        contentType: "application/json; charset=utf-8",
        dataType: "XML",
        success: function (response) {
            $("#xmlText").text(response.xml);
        error: function (msg) {
            alert(msg.toString);
WCF Interface:
[OperationContract]
        [WebInvoke(Method = "POST", BodyStyle = WebMessageBodyStyle.Wrapped, ResponseFormat = WebMessageFormat.Xml, RequestFormat = WebMessageFormat.Json,
                    UriTemplate = "GetSearchResults")]
        XElement GetSearchResults(inputParameters parameters);
        [OperationContract]
        [WebInvoke(Method = "POST", RequestFormat = WebMessageFormat.Json, UriTemplate = "getFile")]
        Stream GetFile(DocInfo info);
Web.config:
 <system.web>
    <compilation debug="true" targetFramework="4.0" />
    <customErrors mode="Off"/>
  </system.web>
 <system.webServer>
    <modules runAllManagedModulesForAllRequests="true"/>
  </system.webServer>
 <system.serviceModel>
   <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true">
   </serviceHostingEnvironment>
   <standardEndpoints>
     <webHttpEndpoint>
       <standardEndpoint name="" helpEnabled="true" automaticFormatSelectionEnabled="true"></standardEndpoint>
     </webHttpEndpoint>
   </standardEndpoints>
 </system.serviceModel>
The service is hosted on IIS6.
When I call the service I get the following error message:
500 System.ServiceModel.ServiceActivationException
I can call the GetFile method and get the response stream but I get the error message when calling GetSearchResults.
Any help will be appreciated.
I encountered this error for the reason mentioned below
Memory gates checking failed because the free memory (258187264 bytes) is less than 5% of total memory.  As a result, the service will not be available for incoming requests.  To resolve this, either reduce the load on the machine or adjust the value of minFreeMemoryPercentageToActivateService on the serviceHostingEnvironment config element.
Related Solutions
REST / SOAP endpoints for a WCF service

You can expose the service in two different endpoints.
the SOAP one can use the binding that support SOAP e.g. basicHttpBinding, the RESTful one can use the webHttpBinding. I assume your REST service will be in JSON, in that case, you need to configure the two endpoints with the following behaviour configuration
<endpointBehaviors>
  <behavior name="jsonBehavior">
    <enableWebScript/>
  </behavior>
</endpointBehaviors>
An example of endpoint configuration in your scenario is 
<services>
  <service name="TestService">
    <endpoint address="soap" binding="basicHttpBinding" contract="ITestService"/>
    <endpoint address="json" binding="webHttpBinding"  behaviorConfiguration="jsonBehavior" contract="ITestService"/>
  </service>
</services>
so, the service will be available at
http://www.example.com/soap
http://www.example.com/json
Apply [WebGet] to the operation contract to make it RESTful.
public interface ITestService
   [OperationContract]
   [WebGet]
   string HelloWorld(string text)
Note, if the REST service is not in JSON, parameters of the operations can not contain complex type.
Reply to the post for SOAP and RESTful POX(XML)
For plain old XML as return format, this is an example that would work both for SOAP and XML.
[ServiceContract(Namespace = "http://test")]
public interface ITestService
    [OperationContract]
    [WebGet(UriTemplate = "accounts/{id}")]
    Account[] GetAccount(string id);
POX behavior for REST Plain Old XML
<behavior name="poxBehavior">
  <webHttp/>
</behavior>
Endpoints
<services>
  <service name="TestService">
    <endpoint address="soap" binding="basicHttpBinding" contract="ITestService"/>
    <endpoint address="xml" binding="webHttpBinding"  behaviorConfiguration="poxBehavior" contract="ITestService"/>
  </service>
</services>
Service will be available at
http://www.example.com/soap
http://www.example.com/xml
REST request
try it in browser,
  
http://www.example.com/xml/accounts/A123
SOAP request
client endpoint configuration for SOAP service after adding the service reference,
  <client>
    <endpoint address="http://www.example.com/soap" binding="basicHttpBinding"
      contract="ITestService" name="BasicHttpBinding_ITestService" />
  </client>
in C#
TestServiceClient client = new TestServiceClient();
client.GetAccount("A123");
Another way of doing it is to expose two different service contract and each one with specific configuration. This may generate some duplicates at code level, however at the end of the day, you want to make it working.
    
Javascript – How to manage a redirect request after a jQuery Ajax call

I read this question and implemented the approach that has been stated regarding setting the response HTTP status code to 278 in order to avoid the browser transparently handling the redirects. Even though this worked, I was a little dissatisfied as it is a bit of a hack.
After more digging around, I ditched this approach and used JSON. In this case, all responses to AJAX requests have the status code 200 and the body of the response contains a JSON object that is constructed on the server. The JavaScript on the client can then use the JSON object to decide what it needs to do.
I had a similar problem to yours. I perform an AJAX request that has 2 possible responses: one that redirects the browser to a new page and one that replaces an existing HTML form on the current page with a new one. The jQuery code to do this looks something like:
$.ajax({
    type: "POST",
    url: reqUrl,
    data: reqBody,
    dataType: "json",
    success: function(data, textStatus) {
        if (data.redirect) {
            // data.redirect contains the string URL to redirect to
            window.location.href = data.redirect;
        } else {
            // data.form contains the HTML for the replacement form
            $("#myform").replaceWith(data.form);
The JSON object "data" is constructed on the server to have 2 members: data.redirect and data.form. I found this approach to be much better.