diff --git a/ChangeLog b/ChangeLog
index 7bd5edc964..5ce6afcf72 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -19,6 +19,7 @@ Enhancements:
 - #6977 Update synergy UI. Configure server
 - #6978 Update synergy UI. Settings window
 - #6981 Update synergy UI. Setup client configuration
+- #6984 Update synergy UI. Client error messages
 - #6962 | #6965 Add macOS 10.13 builder
 ===========
 
diff --git a/src/gui/src/ClientConnection.cpp b/src/gui/src/ClientConnection.cpp
new file mode 100644
index 0000000000..71207a5c44
--- /dev/null
+++ b/src/gui/src/ClientConnection.cpp
@@ -0,0 +1,71 @@
+/*
+ * synergy -- mouse and keyboard sharing utility
+ * Copyright (C) 2012-2021 Symless Ltd.
+ * Copyright (C) 2008 Volker Lanz (vl@fidra.de)
+ *
+ * This package is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * found in the file LICENSE that should have accompanied this file.
+ *
+ * This package is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "ClientConnection.h"
+
+#include "MainWindow.h"
+
+#include <QMessageBox>
+#include <QHostAddress>
+
+ClientConnection::ClientConnection(MainWindow& parent) :
+    m_parent(parent)
+{
+}
+
+void ClientConnection::update(const QString& line)
+{
+    if (line.contains("failed to connect to server") &&
+        checkMainWindow())
+    {
+        m_parent.stopSynergy();
+
+        QMessageBox message(&m_parent);
+        message.addButton(QObject::tr("Close"), QMessageBox::RejectRole);
+        message.setText(getMessage());
+        message.exec();
+    }
+}
+
+bool ClientConnection::checkMainWindow()
+{
+    bool result = m_parent.isActiveWindow();
+
+    if (m_parent.isMinimized() || m_parent.isHidden())
+    {
+        m_parent.showNormal();
+        m_parent.activateWindow();
+        result = true;
+    }
+
+    return result;
+}
+
+QString ClientConnection::getMessage() const
+{
+    QString message(QObject::tr("We can’t connect to the server IP address.\nCheck your IP on your server and your firewall settings."));
+
+    QHostAddress address(m_parent.appConfig().getServerHostname());
+    if (address.isNull())
+    {
+        message = QObject::tr("We can’t connect to the server \"%1\" try to connect using the server IP address and check your firewall settings.")
+                           .arg(m_parent.appConfig().getServerHostname());
+    }
+
+    return message;
+}
diff --git a/src/gui/src/ClientConnection.h b/src/gui/src/ClientConnection.h
new file mode 100644
index 0000000000..0d52e95a7d
--- /dev/null
+++ b/src/gui/src/ClientConnection.h
@@ -0,0 +1,39 @@
+/*
+ * synergy -- mouse and keyboard sharing utility
+ * Copyright (C) 2012-2021 Symless Ltd.
+ * Copyright (C) 2008 Volker Lanz (vl@fidra.de)
+ *
+ * This package is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * found in the file LICENSE that should have accompanied this file.
+ *
+ * This package is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef CLIENTCONNECTION_H
+#define CLIENTCONNECTION_H
+
+#include <QString>
+
+class MainWindow;
+
+class ClientConnection
+{
+    MainWindow& m_parent;
+
+public:
+    explicit ClientConnection(MainWindow& parent);
+    void update(const QString& line);
+
+private:
+    QString getMessage() const;
+    bool checkMainWindow();
+};
+
+#endif // CLIENTCONNECTION_H
diff --git a/src/gui/src/MainWindow.cpp b/src/gui/src/MainWindow.cpp
index 423ae21141..f02ca2462a 100644
--- a/src/gui/src/MainWindow.cpp
+++ b/src/gui/src/MainWindow.cpp
@@ -113,7 +113,8 @@ MainWindow::MainWindow (AppConfig& appConfig,
     m_pCancelButton(NULL),
     m_ExpectedRunningState(kStopped),
     m_SecureSocket(false),
-    m_serverConnection(*this)
+    m_serverConnection(*this),
+    m_clientConnection(*this)
 {
 #if !defined(SYNERGY_ENTERPRISE) && defined(SYNERGY_AUTOCONFIG)
     m_pZeroconf = new Zeroconf(this);
@@ -456,6 +457,7 @@ void MainWindow::checkConnected(const QString& line)
     }
     else
     {
+        m_clientConnection.update(line);
         m_pLabelClientState->updateClientState(line);
     }
 
diff --git a/src/gui/src/MainWindow.h b/src/gui/src/MainWindow.h
index 18e11416f2..d3a444eec8 100644
--- a/src/gui/src/MainWindow.h
+++ b/src/gui/src/MainWindow.h
@@ -29,6 +29,7 @@
 
 #include "ServerConfig.h"
 #include "ServerConnection.h"
+#include "ClientConnection.h"
 #include "AppConfig.h"
 #include "VersionChecker.h"
 #include "IpcClient.h"
@@ -69,6 +70,7 @@ class MainWindow : public QMainWindow, public Ui::MainWindowBase
     friend class ActivationDialog;
     friend class SettingsDialog;
     friend class ServerConnection;
+    friend class ClientConnection;
 
     public:
         enum qSynergyState
@@ -241,6 +243,7 @@ public slots:
         bool                m_SecureSocket;             // brief Is the program running a secure socket protocol (SSL/TLS)
         QString             m_SecureSocketVersion;      // brief Contains the version of the Secure Socket currently active
         ServerConnection    m_serverConnection;
+        ClientConnection    m_clientConnection;
 
         void                updateAutoConfigWidgets();
         
diff --git a/src/gui/src/ServerConnection.cpp b/src/gui/src/ServerConnection.cpp
index 03a2a9d0bb..fba9b62c44 100644
--- a/src/gui/src/ServerConnection.cpp
+++ b/src/gui/src/ServerConnection.cpp
@@ -45,13 +45,16 @@ void ServerConnection::update(const QString& line)
 
 bool ServerConnection::checkMainWindow()
 {
+    bool result = m_parent.isActiveWindow();
+
     if (m_parent.isMinimized() || m_parent.isHidden())
     {
         m_parent.showNormal();
         m_parent.activateWindow();
+        result = true;
     }
 
-    return m_parent.isActiveWindow();
+    return result;
 }
 
 void ServerConnection::addClient(const QString& clientName)