Qt doesn't see include class

Question

I have strange problem with including class. I have the class: main.cpp:

#include "startwidget.h"
#include <QApplication>
#include <QtPlugin>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    StartWidget w;
    w.show();

    return a.exec();
}

startwidget.h:

#ifndef STARTWIDGET_H
#define STARTWIDGET_H

#include <QWidget>
#include "phonewidget.h"
#include "servicearealogin.h"

namespace Ui {
class StartWidget;
}

class StartWidget : public QWidget
{
    Q_OBJECT

public:
    explicit StartWidget(QWidget *parent = 0);
    ~StartWidget();

private:
    Ui::StartWidget *ui;

    PhoneWidget *phoneWidget;
    ServiceAreaLogin *serviceAreaLogin;
};

#endif // STARTWIDGET_H

servicearealogin.h:

#ifndef SERVICEAREALOGIN_H
#define SERVICEAREALOGIN_H

#include <QWidget>
#include <QTimer>
#include "startwidget.h"

namespace Ui {
class ServiceAreaLogin;
}

class ServiceAreaLogin : public QWidget
{
    Q_OBJECT

public:
    explicit ServiceAreaLogin(QWidget *parent = 0);
    ~ServiceAreaLogin();

private:
    Ui::ServiceAreaLogin *ui;
    StartWidget *startWidget;

    void startWidgetInit();

#endif // SERVICEAREALOGIN_H

The problem is that when I want to compile my program I get a error:

/main.cpp:1: In file included from ../Fluidwash/main.cpp:1:

/startwidget.h:6: In file included from startwidget.h:6:

servicearealogin.h:22: błąd: unknown type name 'StartWidget' StartWidget *startWidget; ^

I really don't understand why it can't find the StartWidget class if I included this in headers.

Or maybe my include politic is bad?

In my StartWidget QWidget I do serviceAreaLogin->show(), now I need do the same with startWidget to back to previous widget.

I read it Resolve header include circular dependencies and for me I included .h of class that i created pointer. So why doesn't it see the class?