Unable to feed lhe file to pythia8

I am trying to feed pythia8 one lhe file which I have created from calchep. The process is DM DM -> H H. The DM is a singlet scalar. I am writing the following code in pythia8,

#include"Pythia8/Pythia.h"
#include<iostream>
#include<sstream>
#include<cmath>
#include<fstream>
#include<numeric>

#include "Pythia8Plugins/FastJet3.h"
#include "fastjet/PseudoJet.hh"
#include "fastjet/ClusterSequence.hh"

using namespace Pythia8;
using namespace std;

using namespace fastjet;

int main()
{

int nEvent = 100000; //number of events we want to generate

Pythia pythia;

Event& event = pythia.event;
pythia.readString("Beams:frameType=4");
pythia.readString("Beams:LHEF=sstohh.lhe");
pythia.readString("LesHouches:setLifetime=2");
pythia.readString("SLHA:minMassSM=0.");

pythia.readString("PartonLevel:FSR=off");
pythia.readString("PartonLevel:ISR=off");
pythia.readString("PartonLevel:MPI=off");

pythia.readString("HadronLevel:Hadronize=on");
pythia.readString("HadronLevel:Decay=on");
pythia.readString("SigmaProcess:renormScale2 = 4");
pythia.readString("SigmaProcess:factorScale2 = 4");

//initialise pythia
pythia.init();

I am getting the following error,

PYTHIA Info from SLHAinterface::initSLHA: No MODSEL found, keeping internal SUSY switched off
 PYTHIA Info from SLHAinterface::initSLHA: importing MASS entries for id = {50800000}
 PYTHIA Warning in SLHAinterface::initSLHA: adding off shell DECAY mode 25 -> 24 -24
 PYTHIA Warning in SLHAinterface::initSLHA: adding off shell DECAY mode 25 -> 23 23
 PYTHIA Info from SLHAinterface::initSLHA: importing DECAY tables for id = {25}
 PYTHIA Error in Pythia::init: could not set up PDF for beam A
 PYTHIA Abort from Pythia::init: PDF initialization failed
 PYTHIA Abort from Pythia::next: not properly initialized so cannot generate events

*------- PYTHIA Event and Cross Section Statistics -------------------------------------------------------------*
 | |
 | Subprocess Code | Number of events | sigma +- delta |
 | | Tried Selected Accepted | (estimated) (mb) |
 | | | |
 |-----------------------------------------------------------------------------------------------------------------|
 | | | |
 | | | |
 | sum | 0 0 0 | 0.000e+00 0.000e+00 |
 | |
 *------- End PYTHIA Event and Cross Section Statistics ----------------------------------------------------------*

 *------- PYTHIA Error and Warning Messages Statistics ----------------------------------------------------------*
 | |
 | times message |
 | |
 | 1 Abort from Pythia::init: PDF initialization failed |
 | 10000 Abort from Pythia::next: not properly initialized so cannot generate events |
 | 1 Error in Pythia::init: could not set up PDF for beam A |
 | 1 Info from SLHAinterface::initSLHA: No MODSEL found, keeping internal SUSY switched off |
 | 1 Info from SLHAinterface::initSLHA: importing DECAY tables |
 | 1 Info from SLHAinterface::initSLHA: importing MASS entries |
 | 2 Warning in SLHAinterface::initSLHA: adding off shell DECAY mode |
 | |
 *------- End PYTHIA Error and Warning Messages Statistics ------------------------------------------------------*

Please let me know what am I missing.