Invalid Menu Handle - ERROR 1401

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C#

I'm using a part of this code to disable hotkeys.

But even after 2 days of lurking around the web, I haven't found a solution for the error 1401 which doesn't disable ALT+TAB, I would ignore this if I could and just put the line of code for ALT+TAB in comentary, but I realy need it to be disabled since I'm running a cybercafe based application.

Using:

using System.Diagnostics; //para poder utilizar a CMD do computador
using System.Runtime.InteropServices; //para poder utilizar a CMD do computador

DLL Library:

#region Dynamic Link Library Imports

[DllImport("user32.dll")]
private static extern int FindWindow(string cls, string wndwText);

[DllImport("user32.dll")]
private static extern int ShowWindow(int hwnd, int cmd);

[DllImport("user32.dll")]
private static extern long SHAppBarMessage(long dword, int cmd);

[DllImport("user32.dll")]
private static extern int RegisterHotKey(IntPtr hwnd, int id, int
fsModifiers, int vk);

[DllImport("user32.dll")]
private static extern int UnregisterHotKey(IntPtr hwnd, int id);

#endregion

Constants and Variables:

#region Modifier Constants and Variables

// Constants for modifier keys
private const int USE_ALT = 1;
private const int USE_CTRL = 2;
private const int USE_SHIFT = 4;
private const int USE_WIN = 8;

// Hot key ID tracker
short mHotKeyId = 0;

#endregion

MainCode to block the hotkeys:

#region


        private void buttonlock()
        {
            // Related browser window key combinations
            // -- Some things that you may want to disable --
            //CTRL+A           Select all
            //CTRL+B           Organize favorites
            //CTRL+C           Copy
            //CTRL+F           Find
            //CTRL+H           View history
            //CTRL+L           Open locate
            //CTRL+N           Open new browser window
            //CTRL+O           Open locate
            //CTRL+P           Print
            //CTRL+R           Refresh
            //CTRL+S           Save
            //CTRL+V           Paste
            //CTRL+W           Close
            //CTRL+X           Cut
            //ALT+F4           Close

            // Use CTRL+ALT+DEL to open the task manager,
            // kill Internet Explorer and then close the application window
            // to exit

            // Disable ALT+F4 - exit
            RegisterGlobalHotKey(Keys.F4, USE_ALT);

            // Disable CTRL+W - exit
            RegisterGlobalHotKey(Keys.W, USE_CTRL);

            // Disable CTRL+N - new window
            RegisterGlobalHotKey(Keys.N, USE_CTRL);

            // Disable CTRL+S - save
            RegisterGlobalHotKey(Keys.S, USE_CTRL);

            // Disable CTRL+A - select all
            RegisterGlobalHotKey(Keys.A, USE_CTRL);

            // Disable CTRL+C - copy
            RegisterGlobalHotKey(Keys.C, USE_CTRL);

            // Disable CTRL+X - cut
            RegisterGlobalHotKey(Keys.X, USE_CTRL);

            // Disable CTRL+V - paste
            RegisterGlobalHotKey(Keys.V, USE_CTRL);

            // Disable CTRL+B - organize favorites
            RegisterGlobalHotKey(Keys.B, USE_CTRL);

            // Disable CTRL+F - find
            RegisterGlobalHotKey(Keys.F, USE_CTRL);

            // Disable CTRL+H - view history
            RegisterGlobalHotKey(Keys.H, USE_CTRL);

            // Disable ALT+Tab - tab through open applications
            RegisterGlobalHotKey(Keys.Tab, USE_ALT);

            // hide the task bar - not a big deal, they can
            // still CTRL+ESC to get the start menu; for that
            // matter, CTRL+ALT+DEL also works; if you need to
            // disable that you will have to violate SAS and 
            // monkey with the security policies on the machine
            ShowWindow(FindWindow("Shell_TrayWnd", null), 0);  
        }



        private void RegisterGlobalHotKey(Keys hotkey, int modifiers)
        {
            try
            {
                // increment the hot key value - we are just identifying
                // them with a sequential number since we have multiples
                mHotKeyId++;

                if (mHotKeyId > 0)
                {
                    // register the hot key combination
                    if (RegisterHotKey(this.Handle, mHotKeyId, modifiers,
                        Convert.ToInt16(hotkey)) == 0)
                    {
                        // tell the user which combination failed to register 
                        // this is useful to you, not an end user; the user
                        // should never see this application run
                        MessageBox.Show("Error: " +
                            mHotKeyId.ToString() + " - " +
                            Marshal.GetLastWin32Error().ToString(),
                            "Hot Key Registration");
                    }
                }
            }
            catch
            {
                // clean up if hotkey registration failed -
                // nothing works if it fails
                UnregisterGlobalHotKey();
            }
        }

        private void UnregisterGlobalHotKey()
        {
            // loop through each hotkey id and
            // disable it
            for (int i = 0; i < mHotKeyId; i++)
            {
                UnregisterHotKey(this.Handle, i);
            }
        }

        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);

            // if the message matches,
            // disregard it
            const int WM_HOTKEY = 0x312;
            if (m.Msg == WM_HOTKEY)
            {
                // Ignore the request or each
                // disabled hotkey combination
            }
        }

#endregion