do res.HttpResponse.Data.Rewind()
set dynObj = {}.%FromJSON(res.HttpResponse.Data)
// now, you can use the JSON-Data
write dynObj.propName  // if it's a dynObject
write dynObj.%Get(0)   // if it's a dynArray

If you want to reorder JSON properties (alphabetically or just put some of them at the beginning) then use a utility method, like this, especially if you have several object(types) to reorder

Class DC.Utility Extends %RegisteredObject
/// Reorder a JSON Object or Array
/// obj:  JSON-Object
/// 	  ord: prop1, prop2, ...	Desired order for (some) properties
/// 	       (Properties not listed are copied in the order in which they were created)
/// 	       If ord not present, properties will be reordered in aplphabetical order
/// obj: JSON-Array
/// 	 ord: pos1, pos2, ...	Desired order for (some) array items
/// 	      (Items not listed are copied in ascending order)
ClassMethod ReOrder(obj As %DynamicAbstractObject, ord... As %String)
	i obj.%Extends("%DynamicObject") {
		s new={}, itr=obj.%GetIterator()
		i '$g(ord) {
			while itr.%GetNext(.k) { s done(k)=0 }
			s k="" f  s k=$o(done(k)) q:k=""  d new.%Set(k,obj.%Get(k))
		} else {
			f i=1:1:$g(ord) { s k=ord(i),done(k)=1 d:$e(obj.%GetTypeOf(k),1,2)'="un" new.%Set(k,obj.%Get(k)) }
			while itr.%GetNext(.k,.v) { d:'$d(done(k)) new.%Set(k,v) }
	} elseif obj.%Extends("%DynamicArray") {
		s new=[], itr=obj.%GetIterator(), max=obj.%Size(), done=""
		f i=1:1:$g(ord) { s k=ord(i) i k,k<=max d new.%Push(obj.%Get(k-1)) s $bit(done,k)=1 }
		while itr.%GetNext(.k,.v) { d:'$bit(done,k+1) new.%Push(v) }
	} else { s new=obj }
	q new

Some examples

s car={"color":"red", "fuel":"diesel", "maxspeed":150, "maker":"Audi", "model":"Quattro Q5", "power":300, "available":true, "rating":8, "allWheel":true }
s car1=##class(DC.Utility).ReOrder(car) // order all props alphabetically
s car2=##class(DC.Utility).ReOrder(car,"maker","model","available") // start with maker, model, etc.

w car.%ToJSON(),!,car1.%ToJSON(),!,car2.%ToJSON() --->
{"color":"red","fuel":"diesel","maxspeed":150,"maker":"Audi","model":"Quattro Q5","power":300,"available":true,"rating":8,"allWheel":true}
{"allWheel":"1","available":"1","color":"red","fuel":"diesel","maker":"Audi","maxspeed":150,"model":"Quattro Q5","power":300,"rating":8}
{"maker":"Audi","model":"Quattro Q5","available":"1","color":"red","fuel":"diesel","maxspeed":150,"power":300,"rating":8,"allWheel":"1"}

Is NOT the same. You can it prove by adding a label to the line with the read command and a new line at the end

    // Use fic
old Read *R:20 Else  Do  Quit    ;;;;  comando else aplicado a read.
    . Use 0 Write !!!,"Expired time."
    If $c(R)="a" d
    . Use 0 Write !!!,"A letter a has been read."
    . Quit
    write !,"If there are more lines, they will be executed",!

    // Use fic
new Read *R:20
    If $Test {
    Use 0 Write !!!,"One character read"
    Else {
    Use 0 Write !!!,"Expired time."
    write !,"If there are more lines, they will be executed",!

now let run both of them...

do old // let the timeout occur
do old // now with some input
do new // let the timeout occur
do new // now with some input

Do you see the difference? If there are more lines (at end) they will be executed in opposite cases (timeout/notimeout)

Things are not so easy as they seem, you have to consider scopes too. Take the above class (DC.LineNumber) and add three more methods:

ClassMethod CaseA(x)
    if x goto zTest
    quit "A0"
zTest quit "A1"

ClassMethod CaseB(x)
    if x goto Test
    quit "B0"
Test quit "B1"

ClassMethod Test()
    write ..CaseA(0),..CaseA(1) set linenumber=..SrcLineNumberFromStack(.routine,.label,.offset,.src) do prt
    write ..CaseB(1),..CaseB(0) set linenumber=..SrcLineNumberFromStack(.routine,.label,.offset,.src) do prt
    // debug
prt	write !,"routine: ",routine
    write !,"label: ",label
    write !,"offset: ",offset
    write !,"linenumber: ",linenumber
    write !,"src:",src,!!

and now do the test:

do ##class(DC.LineNumber).Test()

and check the output... 

OK, I know, this is a (very) constructed case and shouldn't coincide with an everyday development style, but who knows, what a mad programer sometimes produces...

If your serial class is named Data.Serial (as in your example code) then you should use the same name for the serial property too

Class Data.Persistent Extends %Persistent
Property MPID as %Integer;
Property Name as Data.Serial;   <--- !!!!!

The correct way to set the values

Set Obj=##Class(Data.Persistent).%New()
Set Obj.Name.FirstName=FirstName   ; <----
Set Obj.Name.LastName=LastName     ; <----
Set tSC=Obj.%Save()

I think, I have a solution for you

ClassMethod GetImage()
	s req=##class(%Net.HttpRequest).%New()
	s req.Server=""
	s req.SSLConfiguration="SSL"
	s req.ReadRawMode=1        //  <<---- this is your solution
	d req.Get("/Web/WebShopImages/landscape_medium/_t/if/sortimentsboxen-1.jpg")
	q req.HttpResponse

To get the image

s rsp=##class(Some.Class).GetImage()
i rsp.StatusCode=200 {
    s file="c:\temp\imageName.jpg"
    o file:"nwu":0
    i $t u file d rsp.Data.Rewind(),rsp.Data.OutputToDevice()
    c file

 That's all...

I never had this kind of problem, but a quick and dirty method would be: 1) remove the 'Mount Read-only' flag, 2) run the tune table utility, 3) reenable the 'Mount Read-only flag'.  I hope, you do not have some mean application, waiting for the chance of his life, to get a writable database...

One of the problems could be the Bas64 encoding. This function inserts after each 76th byte a CRLF which possibly confuses the other party. Try with 

Set EncryptedBase64=$SYSTEM.Encryption.Base64Encode(encrypted, 1)

The parameter 1 says, do not insert CRLFs. Also, the text you encrypt must be an ANSI (8bit) text. If you are on a unicode system, you should call

Set encrypted=$SYSTEM.Encryption.AESCBCEncrypt($zcvt(text,"O","UTF8"),key,iv)

You are just one letter away from solution...

set db=##Class(SYS.Database).%OpenId("/trak/base/tc/db/ct",,.sc)
//................................^^^  Id, not ID!

I do not use Ensemble, but I would try using the JSON-Adaptor, something like this

Class MessageB Extends (Ens.Request, %JSON.Adaptor)
   Property ClientId As %String(MAXLEN = "");
   Property message As %Stream.TmpBinary;

For example

s r=##class(MessageB).%New()
s r.ClientId=12345
d r.message.Write("part1")
d r.message.Write("part2")
w r.%JSONExportToStream(.s)
d s.Rewind()
w s.Read(s.Size) --> {"ClientId":"12345","message":"cGFydDFwYXJ0Mg=="}