RooFit Convolution basic problem

ROOT
1

I am having a simple problem of convolving a model with a pdf.
could anyone give some advice?

void powerlaw()
{
  RooRealVar x("x","Energy",0.1,20) ; // use x, if E - > bad expression name                        
  RooRealVar G("G","slope",-2,-4,-1) ;
  RooRealVar N("N","normalisation",1e-12,1e-13,1e-11) ;
  RooFormulaVar flux("flux","N*pow(x,G)",RooArgSet(N,x,G)) ;
  RooRealVar a0("a0","a0",4.73968) ;
  RooRealVar a1("a1","a1",0.329175) ;
  RooRealVar a2("a2","a2",-0.129551) ;
  RooRealVar a3("a3","a3",-0.463194) ;
  RooRealVar a4("a4","a4",-0.0861036) ;
  RooRealVar a5("a5","a5", 1.02192) ;
  RooRealVar a6("a6","a6",-0.614789) ;
  RooRealVar a7("a7","a7",-0.155646) ;
  RooRealVar a8("a8","a8",0.208511) ;
  RooRealVar a9("a9","a9",-0.0434517) ;
  RooGenericPdf area("area","Effective Area","pow(10,a0)*pow(x,a1)*pow(x,a2*log10(x))*pow(x,a3*log10(x)*log10(x))*pow(x,a4*pow(log10(x),3))*pow(x,a5*pow(log10(x),4))*pow(x,a6*pow(log10(x),5))*pow(x,a7*pow(log10(x),6))",RooArgSet(a0,x,a1,a2,a3,a4,a5,a6,a7)) ;
  x.setBins(1000,"cache") ;
  RooFFTConvPdf lxa("lxa","flux (X) area",x,flux,area) ;
  RooDataSet* data = lxa.generate(x,10000) ;
  lxa.fitTo(*data) ;
  RooPlot* frame = x.frame(Title("Flux")) ;
  RooPlot* frame1 = x.frame(Title("Area")) ;
  RooPlot* frame2 = x.frame(Title("Convolution")) ;
  data->plotOn(frame,MarkerColor(kGreen)) ;
  flux.plotOn(frame,LineStyle(7),LineWidth(2),LineColor(7)) ;
  area.plotOn(frame1,LineStyle(1),LineWidth(2),LineColor(6)) ;
  lxa.plotOn(frame2,LineWidth(2),LineColor(4)) ;
  TCanvas* m = new TCanvas("convolution","convolution",1200,600) ;
  m->Divide(2);
  m->cd(1);
  gPad->SetLeftMargin(0.15) ; frame->GetYaxis()->SetTitleOffset(1.4) ;
  frame->Draw() ;
  gPad->SetLogy();   gPad->SetLogx();
  m->cd(2);
  gPad->SetLogy();   gPad->SetLogx();
  frame1->Draw() ;
  m->cd(3);
  frame2->Draw() ;
}

The output is:

Error: Can't call RooFFTConvPdf::RooFFTConvPdf("lxa","flux (X) area",x,flux,area) in current scope powerlaw.C:32:
2

My fftw3 libraries were missing. Just had to recompile with --enable–fftw3 and its directories.