Simple DetourLibrary Fails for Messagebox Hook

i am trying to do a simple MessageBox Hook for x86 I happened to follow https://github.com/MalwareTech/BasicHook/blob/master/BasicHook/hook.cpp and i have been able to work until something like what i have now . But when i do a simple Messagebox Hook, i get an Access violation Error.

My code looks somewhat like this :

SHook.h

#pragma once

#include <stdio.h>
#include <stdlib.h>
#include <Windows.h>
#include "hde32.h"

class SHook
{
private :
    LPVOID FunctionAddress;
    DWORD TrampolineLength = 0, OriginalProtection;
    hde32s disam;
    PBYTE pTrampBackup;
    BYTE Jump[5] = { 0xE9, 0x00, 0x00, 0x00, 0x00 };
public:
    BOOL SetHook(LPCSTR dll, LPCSTR name, LPVOID proxy, LPVOID original, PDWORD length);
};

For SHook.cpp

#include "SHook.h"

BOOL SHook::SetHook(LPCSTR dll, LPCSTR name, LPVOID proxy, LPVOID original, PDWORD length)
{
    FunctionAddress = GetProcAddress(GetModuleHandleA(dll), name);
    if (!FunctionAddress)
        return FALSE;

    //disassemble length of each instruction, until we have 5 or more bytes worth
    while (TrampolineLength < 5)
    {
        LPVOID InstPointer = (LPVOID)((DWORD)FunctionAddress + TrampolineLength);
        TrampolineLength += hde32_disasm(InstPointer, &disam);
    }


    //Build the trampoline buffer
    pTrampBackup = static_cast<PBYTE>(VirtualAlloc(nullptr, TrampolineLength + 6, MEM_COMMIT, PAGE_EXECUTE_READWRITE));
    memcpy(pTrampBackup, FunctionAddress, TrampolineLength); 
    *(DWORD*)(Jump + 1) = ((DWORD)FunctionAddress + TrampolineLength) - ((DWORD)original + TrampolineLength + 5);
    memcpy((LPVOID)((DWORD)original + TrampolineLength), Jump, 5);
    //memcpy(pTrampBackup + TrampolineLength, Jump, 5); --> This fired an Exception for Null pointers

    //Make sure the function is writable
    if (!VirtualProtect(FunctionAddress, TrampolineLength, PAGE_EXECUTE_READWRITE, &OriginalProtection))
        return FALSE;

    //Build and atomically write the hook
    *(DWORD*)(Jump + 1) = (DWORD)proxy - (DWORD)FunctionAddress - 5;
    //SafeMemcpyPadded(FunctionAddress, Jump, 5);

    //Restore the original page protection
    VirtualProtect(FunctionAddress, TrampolineLength, OriginalProtection, &OriginalProtection);

    //Clear CPU instruction cache
    FlushInstructionCache(GetCurrentProcess(), FunctionAddress, TrampolineLength);

    *length = TrampolineLength;
    return TRUE;
}

And in the basic Implementation for a simple Messagebox

#include <stdio.h>
#include <Windows.h>
#include <intrin.h>
#include <string>
#include "SHook.h"

typedef int (WINAPI* TdefOldMessageBoxA)(HWND hWnd, LPCSTR lpText, LPCTSTR lpCaption, UINT uType);
TdefOldMessageBoxA myOldMessageBoxA;

SHook shook;
int WINAPI HookMessageBoxA(HWND hWnd, LPCSTR lpText, LPCTSTR lpCaption, UINT uType) 
{
    MessageBoxA(NULL, "Hooked", "Hooked", MB_OK);
    return myOldMessageBoxA(hWnd, lpText, lpCaption, uType);
}

void EstablishHook()
{
        myOldMessageBoxA = (TdefOldMessageBoxA)& MessageBoxA;
        shook.SetHook("user32.dll","MessageBoxA", (LPVOID)&HookMessageBoxA, myOldMessageBoxA,0);
}

int main() 
{
    EstablishHook();
}

Now the Exception is fired on this line particularly

memcpy((LPVOID)((DWORD)original + TrampolineLength), Jump, 5);

This is the Exception as it looks like :

Exception thrown at 0x0F2B3839 (vcruntime140d.dll) in SHook.exe: 0xC0000005: Access violation writing location 0x75C51F75.

Could there be something i am missing here?