Fix for issue #112

GBM/Forms/frmMain.vb

@@ -1826,8 +1826,18 @@ Public Class frmMain
     End Sub
 
     Private Sub Main_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
+        Dim oMutex As New System.Threading.Mutex
+        Dim bNewInstance As Boolean
+
         'Init
         Try
+            oMutex = New System.Threading.Mutex(True, "GameBackupMonitor", bNewInstance)
+
+            'Ensure only one instance is running
+            If Not bNewInstance Then
+                mgrCommon.ShowMessage(frmMain_ErrorAlreadyRunning, MsgBoxStyle.Exclamation)
+                ShutdownApp(False)
+            Else
                 SetForm()
                 VerifyGameDataPath()
                 LoadAndVerify()
@@ -1855,7 +1865,11 @@ Public Class frmMain
                     Else
                         Me.gMonTray.Visible = True
                     End If
+
+                    GC.KeepAlive(oMutex)
                 End If
+            End If
+
         Catch ex As Exception
             If mgrCommon.ShowMessage(frmMain_ErrorInitFailure, ex.Message, MsgBoxStyle.YesNo) = MsgBoxResult.No Then
                 bInitFail = True

GBM/My Project/Resources.Designer.vb

@@ -2832,6 +2832,15 @@ Namespace My.Resources
             End Get
         End Property
         
+        '''<summary>
+        '''  Looks up a localized string similar to An instance of Game Backup Monitor is already running..
+        '''</summary>
+        Friend ReadOnly Property frmMain_ErrorAlreadyRunning() As String
+            Get
+                Return ResourceManager.GetString("frmMain_ErrorAlreadyRunning", resourceCulture)
+            End Get
+        End Property
+        
         '''<summary>
         '''  Looks up a localized string similar to GBM is running from a new location, the Windows startup entry has been updated..
         '''</summary>

GBM/My Project/Resources.resx

@@ -1945,4 +1945,7 @@
   <data name="frmSettings_chkSessionTracking" xml:space="preserve">
     <value>Enable session tracking</value>
   </data>
+  <data name="frmMain_ErrorAlreadyRunning" xml:space="preserve">
+    <value>An instance of Game Backup Monitor is already running.</value>
+  </data>
 </root>