Estou usando uma classe de gancho de teclado global. Esta classe permite verificar se a tecla do teclado foi pressionada em algum lugar. E depois de algum tempo, estou tendo um erro:

        **CallbackOnCollectedDelegate was detected**

A callback was made on a garbage collected delegate of type 'Browser!Utilities.globalKeyboardHook+keyboardHookProc::Invoke'. This may cause application crashes, corruption and data loss. When passing delegates to unmanaged code, they must be kept alive by the managed application until it is guaranteed that they will never be called.

Aqui está a classe globalkeyboardHook:

        public delegate int keyboardHookProc(int code, int wParam, ref keyboardHookStruct lParam);

        public struct keyboardHookStruct
        {
            public int vkCode;
            public int scanCode;
            public int flags;
            public int time;
            public int dwExtraInfo;
        }

        const int WH_KEYBOARD_LL = 13;
        const int WM_KEYDOWN = 0x100;
        const int WM_KEYUP = 0x101;
        const int WM_SYSKEYDOWN = 0x104;
        const int WM_SYSKEYUP = 0x105;

        public List<Keys> HookedKeys = new List<Keys>();

        IntPtr hhook = IntPtr.Zero;

        public event KeyEventHandler KeyDown;
        public event KeyEventHandler KeyUp;

        public globalKeyboardHook()
        {
            hook();
        }

        ~globalKeyboardHook()
        {
            unhook();
        }

        public void hook()
        {
            IntPtr hInstance = LoadLibrary("User32");
            hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, hInstance, 0);
        }

        public void unhook()
        {
            UnhookWindowsHookEx(hhook);
        }

        public int hookProc(int code, int wParam, ref keyboardHookStruct lParam)
        {
            if (code >= 0)
            {
                Keys key = (Keys)lParam.vkCode;
                if (HookedKeys.Contains(key))
                {
                    KeyEventArgs kea = new KeyEventArgs(key);
                    if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (KeyDown != null))
                    {
                        KeyDown(this, kea);
                    }
                    else if ((wParam == WM_KEYUP || wParam == WM_SYSKEYUP) && (KeyUp != null))
                    {
                        KeyUp(this, kea);
                    }
                    if (kea.Handled)
                        return 1;
                }
            }
            return CallNextHookEx(hhook, code, wParam, ref lParam);
        }

        [DllImport("user32.dll")]
        static extern IntPtr SetWindowsHookEx(int idHook, keyboardHookProc callback, IntPtr hInstance, uint threadId);


        [DllImport("user32.dll")]
        static extern bool UnhookWindowsHookEx(IntPtr hInstance);

        [DllImport("user32.dll")]
        static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref keyboardHookStruct lParam);

        [DllImport("kernel32.dll")]
        static extern IntPtr LoadLibrary(string lpFileName);
        #endregion

Alguma idéia de como consertar isso? O programa funciona bem, mas após algum tempo o programa congela e recebo esse err