Multidesk program doesn't work

[Null]

Hello, I wrote a desktop switching program but it doesn't work:

// deskman.hpp
#include <string>
#include <windows.h>
#include <vector>



#define ERR_ALREADY_EXISTS   1
#define ERR_NOT_EXISTS       2
#define ERR_CREATE           3
#define ERR_SWITCH           4



struct DESKTOP_DATA
{
HDESK hDesk;
std::string name;
};


class DesktopManager
{
protected:
  friend BOOL CALLBACK fed_clbk(LPSTR name,LPARAM lparam);
  std::vector<DESKTOP_DATA>desktops;
  int active_desktop;

  int add_desktop(const DESKTOP_DATA);
  void find_existing_desktops();

  DESKTOP_DATA &get_desktop_by_name(std::string name);
  DESKTOP_DATA &get_desktop_by_number(int i);

public:
  DesktopManager();
  int AddDesktop(std::string name);

  void RemoveDesktop(int desk);
  void RemoveDesktop(std::string name);

  int SetActive(int desk);
  int SetActive(std::string name);

  DESKTOP_DATA EnumDesktop(int i);

  int NumberOfDesktops();

};

// deskman.cpp
#include "deskman.hpp"
#include <windows.h>
#include <iostream>
using namespace std;

void LastError() ;


DesktopManager::DesktopManager()
{
   active_desktop=0;
   find_existing_desktops();

}

int DesktopManager::AddDesktop(string name)
{
    DESKTOP_DATA tmp;
    tmp.hDesk=CreateDesktop(name.c_str(),NULL,NULL,GENERIC_ALL,DESKTOP_CREATEWINDOW,0);
    if(tmp.hDesk==INVALID_HANDLE_VALUE)
          return ERR_CREATE;

    tmp.name=name;
    return add_desktop(tmp);

}


int DesktopManager::NumberOfDesktops()
{
    return desktops.size();
}


DESKTOP_DATA DesktopManager::EnumDesktop(int i)
{
   if(i>desktops.size())
       throw(ERR_NOT_EXISTS);
   return desktops[i];
}


int DesktopManager::SetActive(int desk)
{
    DESKTOP_DATA dt;
    dt=get_desktop_by_number(desk);
    if(!SwitchDesktop(dt.hDesk))
        return ERR_SWITCH;
    SetThreadDesktop(dt.hDesk);
    return 0;
}


int DesktopManager::SetActive(std::string name)
{
    DESKTOP_DATA dt;
    try
      {
        dt=get_desktop_by_name(name);
      }
    catch(...)
     {
         return ERR_NOT_EXISTS;
     }
    if(!SwitchDesktop(dt.hDesk)) // --- ERROR HERE -----
      {
          if(GetLastError()!=0)
              LastError();

          return ERR_SWITCH;
      }

    SetThreadDesktop(dt.hDesk);
    return 0;
}




// ---------------------------------------------------------------

BOOL CALLBACK fed_clbk(LPSTR name,LPARAM lparam)
{
DesktopManager *dm=reinterpret_cast<DesktopManager*>(lparam);
DESKTOP_DATA dt;

dt.name=name;
dt.hDesk=OpenDesktop(name,0,0,GENERIC_ALL);

dm->add_desktop(dt);

return TRUE;
}


void DesktopManager::find_existing_desktops()
{
EnumDesktops(0,fed_clbk,(LPARAM)this);
}


int DesktopManager::add_desktop(const DESKTOP_DATA dt)
{
    for(int i=0;i<desktops.size();i++)
      {
          if(desktops[i].name==dt.name)
              return ERR_ALREADY_EXISTS;
      }
    desktops.push_back(dt);
    return 0;
}


DESKTOP_DATA &DesktopManager::get_desktop_by_name(std::string name)
{
  for(int i=0;i<NumberOfDesktops();i++)
    {
        if(desktops[i].name==name)
            return desktops[i];
    }
throw(ERR_NOT_EXISTS);
}

DESKTOP_DATA &DesktopManager::get_desktop_by_number(int i)
{
    if(i>NumberOfDesktops())
        throw(ERR_NOT_EXISTS);

    return desktops[i];
}






// ------------------
void LastError()
{
    // Retrieve the system error message for the last-error code

    LPVOID lpMsgBuf;
    LPVOID lpDisplayBuf;
    DWORD dw = GetLastError();

    FormatMessage(
        FORMAT_MESSAGE_ALLOCATE_BUFFER |
        FORMAT_MESSAGE_FROM_SYSTEM |
        FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,
        dw,
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPSTR) &lpMsgBuf,
        0, NULL );


    cerr <<"GetLastError returned "<<dw<<": "<<(const char*)lpMsgBuf<<endl;


    LocalFree(lpMsgBuf);
    LocalFree(lpDisplayBuf);
    ExitProcess(dw);
}

// main.cpp
#include <iostream>
#include <windows.h>

#include "deskman.hpp"
using namespace std;




int main()
{
DesktopManager dm;

if(dm.AddDesktop("mydesk")!=0)
  {
    cerr <<"Could not create a desktop"<<endl;
    exit(1);
  }




cout <<"Desktops found on this computer: "<<endl;
DESKTOP_DATA tmp;
for(int i=0;i<dm.NumberOfDesktops();i++)
  {
     tmp=dm.EnumDesktop(i);
     cout <<tmp.name<<endl;
  }

cout <<"--------------------------------"<<endl<<endl;


int ret=dm.SetActive("mydesk"); // This function fails

if(ret==ERR_NOT_EXISTS)
  {
      cerr <<"Desktop doesn't exist"<<endl;
      exit(2);
  }

Sleep(5000);



    return 0;
}

GetLastError from DesktopManager::SetActive always returns 5 (program outputs "GetLastError returned 5: Access is denied.")
What's wrong here?

Thanks for help.