Problem with Calling Custom Action on Custom Ribbon Button to PhoneCall Entity

function ExecuteAction(entityId, entityName, requestName) {
    // Creating the request XML for calling the Action
    var requestXML = ""
    requestXML += "<s:envelope xmlns:s="\"schemas.xmlsoap.org/.../envelope\"">";
    requestXML += "  <s:body>";
    requestXML += "    <execute xmlns="\"schemas.microsoft.com/.../Services\"" xmlns:i="\"www.w3.org/.../XMLSchema-instance\"">";
    requestXML += "      <request xmlns:a="\"schemas.microsoft.com/.../Contracts\"">";
    requestXML += "        <a:parameters xmlns:b="\"schemas.datacontract.org/.../System.Collections.Generic\"">";
    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 += "            </a:name></b:value>";
    requestXML += "          </a:keyvaluepairofstringanytype>";
    requestXML += "        </a:parameters>";
    requestXML += "        <a:requestid i:nil="\"true\"">";
    requestXML += "        <a:requestname>" + requestName + "</a:requestname>";
    requestXML += "      </a:requestid></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", "schemas.microsoft.com/.../Execute");
    req.send(requestXML);

    //Get the Response 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;
}

function openPhoneCall() {

    var entityId = Xrm.Page.data.entity.getId();
    var entityName = "phonecall";
    var requestName = "new_ReactivePhoneCall";

    ExecuteAction(entityId, entityName, requestName);
	window.location.reload(true);
}