PROBLEM INCLUDING 'QSystemInfo' HEADER FILE

[Rakula]

I am working on my first Qt project using the beta version of Qt 4.6 (I had a problem installing the final version). I am writing an application intended only for Symbian mobile devices and I want it to detect whether the device has a touch screen or not. I pasted the following code snippet from the documentation (the page entitled 'Quickstart Example' ).

#ifdef Q_OS_SYMBIAN
    #include <qsysteminfo.h>
    #else
    #include <QSystemInfo> //(1)
    #endif
    using namespace QtMobility; //(2)

#ifdef Q_OS_SYMBIAN
    #include <qsysteminfo.h>
    #else
    #include <QSystemInfo> //(1)
    #endif
    using namespace QtMobility; //(2)

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However, I get a compiler error 'cannot open include file: 'QSystemInfo': (see attachment). I have done the same thing before without any problem. How should I proceed? Several related questions are as follows:- An attempt to load the final version of Qt 4.6 failed. (I can provide a snap-shot of the screen message later if appropriate). Should I uninstall the beta version before installing the final version? If I have developed a project on the beta version, can I build it on the final version?