Undefined reference to signal when linking static library

Hi, all. I'm writing a dynamic library and an application that uses it.
When I compile the library everything seems to be ok, no error messages. But when I compile the application, linker prints the following message:
undefined reference to dbConnected(QString). dbConnected is a signal in my library.
I have tried many things (qmake && make, generate & link *.prl) but the problem stays the same.

Dynamic Library project file:

Code:

#-------------------------------------------------
#
# Project created by QtCreator 2012-07-31T02:34:49
#
#-------------------------------------------------
 
QT       += sql
 
QT       -= gui
 
TARGET = DatabaseTools
TEMPLATE = lib
 
DEFINES += DATABASETOOLS_LIBRARY
 
SOURCES += DatabaseTools.cpp \
    DatabaseObject.cpp \
    DatabaseQuery.cpp \
    DatabaseMutex.cpp \
    DatabaseQueryResult.cpp \
    DatabaseThread.cpp \
    DatabaseQueue.cpp \
    DatabaseHandle.cpp
 
HEADERS += DatabaseTools_global.h \
    DatabaseTools.h \
    DatabaseObject.h \
    DatabaseQuery.h \
    DatabaseMutex.h \
    DatabaseQueryResult.h \
    DatabaseThread.h \
    DatabaseQueue.h \
    DatabaseHandle.h
 
INCLUDEPATH += /usr/include/mysql
LIBS += -lmysqlclient
 
DLLDESTDIR = ../Build
DESTDIR = ../Build
CONFIG += create_prl

Class header file:

Code:

#ifndef DATABASETOOLS_H
#define DATABASETOOLS_H
 
#include "DatabaseTools_global.h"
#include <QObject>
#include <QPointer>
#include <QStringList>
#include <QMap>
#include <QTimer>
 
#include "DatabaseHandle.h"
#include "DatabaseQueue.h"
#include "DatabaseThread.h"
#include "DatabaseQuery.h"
#include "DatabaseObject.h"
 
 
class DATABASETOOLSSHARED_EXPORT DatabaseTools : public QObject
{
    static QMap<QString, QPointer<DatabaseTools> > PointersMap;
 
    QTimer* UpdateTimer;
    DatabaseHandle DbHandle;
    DatabaseQueue DbQueue;
 
    QString SessionUserName, SessionPassword;
 
    bool IsDbEmpty;
    QString DbVersion;
    QString SupportedVersion;
    QStringList UsersNamesList;
    QString SessionId;
 
    QString ConnectionName;
 
    DatabaseTools (QString connection_name);
 
public:
 
    static QPointer<DatabaseTools>& getInstace(QString connection_name);
    static void setAllMultiThreaded (bool multithreaded_operations);
 
    void setMultiThreaded (bool multithreaded_operations);
 
    void connect ();
    void close ();
    void login ();
    void logout ();
    void suspend ();
 
    bool isConnected ();
 
    QString connectionName ();
 
    void setDbAuthParams (QString host_name, QString user_name, QString password);
    void setDbPort (int port);
    void setSessionAuthParams (QString user_name, QString password);
 
signals:
 
    void dbConnected (QString connection_name);
    void dbClosed (QString connection_name);
    void dbOperating (QString connection_name);
    void dbReady (QString connection_name);
 
private slots:
 
    void DatabaseThread_finished (DatabaseThread* thread);
    void DatabaseObject_connected ();
    void DatabaseObject_closed ();
 
};
 
 
#endif // DATABASETOOLS_H

Application project file:

Code:

#-------------------------------------------------
#
# Project created by QtCreator 2012-07-30T20:05:45
#
#-------------------------------------------------
 
QT       += core gui sql
 
TARGET = FitnessCenter-Application
TEMPLATE = app
 
LIBS += -L/home/zzz9/Projects/FitnessCenter/Build -lDatabaseTools
 
SOURCES += main.cpp\
        MainWindow.cpp \
    SetupWizard.cpp \
    ../Widgets/DatabaseStateWidget.cpp
 
HEADERS  += MainWindow.h \
    SetupWizard.h \
    ../Widgets/DatabaseStateWidget.h
 
FORMS    += MainWindow.ui \
    SetupWizard.ui \
    ../Widgets/DatabaseStateWidget.ui
 
RESOURCES += \
    ../Pixmaps/Pixmaps.qrc
 
OTHER_FILES += \
    ÐÐ°Ð¿Ð¾Ð¼Ð¸Ð½Ð°Ð½Ð¸Ñ.txt
 
DESTDIR = ../Build
 
CONFIG += link_prl

Added after 19 minutes:

application and lib are in debug