you are firing asynchronous call may be that's the reason you are not receiving the result immediately . change the below line of the code
Replace : xmlhttp.open("Post", serverUrl, true);
To : xmlhttp.open("Post", serverUrl, false);
If this does not work here is the function that works with out any issue in my environment
function GenerateQuoteFromOpportunityRequest(opportunityid) {
var requestMain = ""
requestMain += "<s:Envelope xmlns:s=\"schemas.xmlsoap.org/.../envelope\">";
requestMain += " <s:Body>";
requestMain += " <Execute xmlns=\"schemas.microsoft.com/.../Services\" xmlns:i=\"www.w3.org/.../XMLSchema-instance\">";
requestMain += " <request i:type=\"b:GenerateQuoteFromOpportunityRequest\" xmlns:a=\"schemas.microsoft.com/.../Contracts\" xmlns:b=\"schemas.microsoft.com/.../Contracts\">";
requestMain += " <a:Parameters xmlns:c=\"schemas.datacontract.org/.../System.Collections.Generic\">";
requestMain += " <a:KeyValuePairOfstringanyType>";
requestMain += " <c:key>OpportunityId</c:key>";
requestMain += " <c:value i:type=\"d:guid\" xmlns:d=\"schemas.microsoft.com/.../Serialization\">"+opportunityid+"</c:value>";
requestMain += " </a:KeyValuePairOfstringanyType>";
requestMain += " <a:KeyValuePairOfstringanyType>";
requestMain += " <c:key>ColumnSet</c:key>";
requestMain += " <c:value i:type=\"a:ColumnSet\">";
requestMain += " <a:AllColumns>true</a:AllColumns>";
requestMain += " <a:Columns xmlns:d=\"schemas.microsoft.com/.../Arrays\" />";
requestMain += " </c:value>";
requestMain += " </a:KeyValuePairOfstringanyType>";
requestMain += " </a:Parameters>";
requestMain += " <a:RequestId i:nil=\"true\" />";
requestMain += " <a:RequestName>GenerateQuoteFromOpportunity</a:RequestName>";
requestMain += " </request>";
requestMain += " </Execute>";
requestMain += " </s:Body>";
requestMain += "</s:Envelope>";
var req = new XMLHttpRequest();
req.open("POST", Xrm.Page.context.getClientUrl() + "/XRMServices/2011/Organization.svc/web", false)
req.setRequestHeader("Accept", "application/xml, text/xml, */*");
req.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
req.setRequestHeader("SOAPAction", "schemas.microsoft.com/.../Execute");
var successCallback = null;
var errorCallback = null;
req.onreadystatechange = function () {
if (req.readyState == 4) {
if (req.status == 200) {
var response = req.responseXML;
alert(response);
}
else {
faultXml=req.responseXML;
var errorMessage = "Unknown Error (Unable to parse the fault)";
if (typeof faultXml == "object") {
try {
var bodyNode = faultXml.firstChild.firstChild;
for (var i = 0; i < bodyNode.childNodes.length; i++) {
var node = bodyNode.childNodes[i];
if ("s:Fault" == node.nodeName) {
for (var j = 0; j < node.childNodes.length; j++) {
var faultStringNode = node.childNodes[j];
if ("faultstring" == faultStringNode.nodeName) {
errorMessage = faultStringNode.text;
break;
}
}
break;
}
}
}
catch (e) { };
}
return new Error(errorMessage);
}
}
};
req.send(requestMain);
}
