SIGSEGV when assigning FILE*

Question

So I have this function that shows a list of contacts separated by pages. The thing is that when the function runs, sometimes makes random fails. So I opened the debugger and the line c=fopen("Contacts.dat","rb"); says SIGSEGV (I know its an error of pointers or such, so i guess it has something to do with FILE*c, but i can't get what the problem is... so here's the code. (Variable names are in spanish, so i changed it a bit for you guys to understand it better).

void listarContactos(){
    struct tContact contact;
    FILE*c;
    c=fopen("Contact.dat","rb");
    if(c==NULL){
        pNULL(4);
        fclose(c);
        exit(1);
    }
    int pageLimit=3;
    int qContacts=0;
    while(fread(&contact,sizeof(tContact),1,c)){
        if(contact.Active){
            qContacts++;
        }
    }
    int aux=0;
    if(qContacts%pageLimit!=0){
        aux=1;
    }
    int vecPag[qContacts/pageLimit+aux];
    int qPages=qContacts/pageLimit+aux;
    fseek(c,0,0);
    vecPag[0]=ftell(c);
    qContacts=0;
    int nPag=0;
    while(fread(&contact,sizeof(tContact),1,c)){
        if(contact.Active){
            qContacts++;
        }
        if(qContacts%pageLimit==0){
            nPag++;
            vecPag[nPag]=ftell(c);
        }
    }
    nPag=0;
    fseek(c,vecPag[nPag],0);
    char choice[4];
    bool exit=0;
    while(!exit){
        system("cls");
        cout<<"CONTACT LIST")<<endl;
        qContacts=0;
        fseek(c,vecPag[nPag],0);
        while(qContacts<pageLimit){
            if(fread(&contact,sizeof(tContact),1,c)){
                if(contact.Active){
                    showContacto(contact);
                    qContacts++;
                }
            }
        }
        cout<<"Page number: "<<nPag+1<<endl;
        cout<<"4 = PREVIOUS PAGE"<<endl;
        cout<<"6 = NEXT PAGE"<<endl;
        cout<<"0 = EXIT"<<endl;
        cout<<"Option: ";
        sys::getline(choice,3);
        switch(choice[0]){
            case '4':{
                if(nPag>0){
                    nPag--;
                }
                break;}
            case '6':{
                if(nPag<qPages){
                    nPag++;
                }
                break;}
            case '0':{      //salir
                exit=1;
                break;}
            default:{
                cout<<"wrong option!"<<endl;
                break;}
        }
    }
    fclose(c);
    return;
}