CRM 2013: Calling actions from javascript

Hi all,

I was trying to call action from javascript using the below code:

function Approve()
{
    debugger;
    var reason = "aaaaaaaaaaaaaaaaaa";
    var entityId = Xrm.Page.data.entity.getId();
    var entityName = "serviceappointment";
    var requestName = "new_SetRejectionReason";
    ExecuteActionCreateProject(reason, entityId, entityName, requestName);
}

function ExecuteActionCreateProject(reason, entityId, entityName, requestName)
{
    // Creating the request XML for calling the Action
    var requestXML = ""
    requestXML += "<s:Envelope xmlns:s=\"http://schemas.xmlsoap.org/soap/envelope/\">";
    requestXML += "  <s:Body>";
    requestXML += "    <Execute xmlns=\"http://schemas.microsoft.com/xrm/2011/Contracts/Services\" xmlns:i=\"http://www.w3.org/2001/XMLSchema-instance\">";
    requestXML += "      <request xmlns:a=\"http://schemas.microsoft.com/xrm/2011/Contracts\">";
    requestXML += "        <a:Parameters xmlns:b=\"http://schemas.datacontract.org/2004/07/System.Collections.Generic\">";
    requestXML += "          <a:KeyValuePairOfstringanyType>";
    requestXML += "            <b:key>Reason</b:key>";
    requestXML += "            <b:value i:type=\"c:string\" xmlns:c=\"http://www.w3.org/2001/XMLSchema\">"+reason+"</b:value>";
    requestXML += "          </a:KeyValuePairOfstringanyType>";
    requestXML += "          <a:KeyValuePairOfstringanyType>";
    requestXML += "            <b:key>Target</b:key>";
    requestXML += "            <b:value i:type=\"a:EntityReference\">";
    requestXML += "              <a:Id>"+entityId+"</a:Id>";
    requestXML += "              <a:LogicalName>"+entityName+"</a:LogicalName>";
    requestXML += "              <a:Name i:nil=\"true\" />";
    requestXML += "            </b:value>";
    requestXML += "          </a:KeyValuePairOfstringanyType>";
    requestXML += "        </a:Parameters>";
    requestXML += "        <a:RequestId i:nil=\"true\" />";
    requestXML += "        <a:RequestName>"+requestName+"</a:RequestName>";
    requestXML += "      </request>";
    requestXML += "    </Execute>";
    requestXML += "  </s:Body>";
    requestXML += "</s:Envelope>";
    var req = new XMLHttpRequest();
    req.open("POST", GetClientUrl(), false)
    req.setRequestHeader("Accept", "application/xml, text/xml, */*");
    req.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
    req.setRequestHeader("SOAPAction", "http://schemas.microsoft.com/xrm/2011/Contracts/Services/IOrganizationServic/Execute");
    req.send(requestXML);
    //Get the Resonse from the CRM Execute method
    var response = req.responseXML.xml;
}
function GetClientUrl() {
    if (typeof Xrm.Page.context == "object") {
        clientUrl = Xrm.Page.context.getClientUrl();
    }
    var ServicePath = "/XRMServices/2011/Organization.svc/web";
    return clientUrl + ServicePath;
}

And this the response that I get:

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Body><s:Fault><faultcode xmlns:a="http://schemas.microsoft.com/ws/2005/05/addressing/none">a:ActionNotSupported</faultcode><faultstring xml:lang="en-US">The message with Action 'http://schemas.microsoft.com/xrm/2011/Contracts/Services/IOrganizationServic/Execute' cannot be processed at the receiver, due to a ContractFilter mismatch at the EndpointDispatcher. This may be because of either a contract mismatch (mismatched Actions between sender and receiver) or a binding/security mismatch between the sender and the receiver.  Check that sender and receiver have the same contract and the same binding (including security requirements, e.g. Message, Transport, None).</faultstring></s:Fault></s:Body></s:Envelope>

Kindly advise