Problem using ReadFile API function, why it doesn't work?

 SafeFileHandle ptrFile = CreateFile("\\\\.\\u:",                     DesiredAccess.GENERIC_READ | DesiredAccess.GENERIC_WRITE,   ShareMode.FILE_SHARE_READ_AND_WRITE, IntPtr.Zero, CreationDisposition.OPEN_EXISTING, FlagsAndAttributes.FILE_ATTRIBUTE_NORMAL, IntPtr.Zero);

uint size = GetFileSize(ptrFile,IntPtr.Zero);
byte[] buffer = new byte[512];
uint readed = 0;
uint a = SetFilePointer(ptrFile, 0, IntPtr.Zero, 0);
ReadFile(ptrFile, buffer,512 , out readed, IntPtr.Zero);

/* ---------------------------------------------------------
 * WINAPI STUFF
 * ------------------------------------------------------ */
        private void ThrowLastWin32Err()
        {
            Marshal.ThrowExceptionForHR(
             Marshal.GetHRForLastWin32Error());
        }
        [Flags]
        public enum DesiredAccess : uint
        {
            GENERIC_READ = 0x80000000,
            GENERIC_WRITE =0x40000000
        }
        [Flags]
        public enum ShareMode : uint
        {
            FILE_SHARE_NONE = 0x0,
            FILE_SHARE_READ = 0x1,
            FILE_SHARE_WRITE = 0x2,
            FILE_SHARE_READ_AND_WRITE = 0x3,            
            FILE_SHARE_DELETE = 0x4,
        }
        public enum MoveMethod : uint
        {
            FILE_BEGIN = 0,
            FILE_CURRENT = 1,
            FILE_END = 2
        }
        public enum CreationDisposition : uint
        {
            CREATE_NEW = 1,
            CREATE_ALWAYS = 2,
            OPEN_EXISTING = 3,
            OPEN_ALWAYS = 4,
            TRUNCATE_EXSTING = 5
        }
        [Flags]
        public enum FlagsAndAttributes : uint
        {
            FILE_ATTRIBUTES_ARCHIVE = 0x20,
            FILE_ATTRIBUTE_HIDDEN = 0x2,
            FILE_ATTRIBUTE_NORMAL = 0x80,
            FILE_ATTRIBUTE_OFFLINE = 0x1000,
            FILE_ATTRIBUTE_READONLY = 0x1,
            FILE_ATTRIBUTE_SYSTEM = 0x4,
            FILE_ATTRIBUTE_TEMPORARY = 0x100,
            FILE_FLAG_WRITE_THROUGH = 0x80000000,
            FILE_FLAG_OVERLAPPED = 0x40000000,
            FILE_FLAG_NO_BUFFERING = 0x20000000,
            FILE_FLAG_RANDOM_ACCESS = 0x10000000,
            FILE_FLAG_SEQUENTIAL_SCAN = 0x8000000,
            FILE_FLAG_DELETE_ON = 0x4000000,
            FILE_FLAG_POSIX_SEMANTICS = 0x1000000,
            FILE_FLAG_OPEN_REPARSE_POINT = 0x200000,
            FILE_FLAG_OPEN_NO_CALL = 0x100000
        }
        public const uint INVALID_HANDLE_VALUE = 0xFFFFFFFF;
        public const uint INVALID_SET_FILE_POINTER = 0xFFFFFFFF;

        // Use interop to call the CreateFile function.
        // For more information about CreateFile,
        // see the unmanaged MSDN reference library.
        [DllImport("kernel32.dll", SetLastError = true)]
        internal static extern SafeFileHandle CreateFile(
         string lpFileName,
         DesiredAccess dwDesiredAccess,
         ShareMode dwShareMode,
         IntPtr lpSecurityAttributes,
         CreationDisposition dwCreationDisposition,
         FlagsAndAttributes dwFlagsAndAttributes,
         IntPtr hTemplateFile);
        [DllImport("kernel32", SetLastError = true)]
        internal static extern bool ReadFile(
         SafeFileHandle hFile,
         Byte[] aBuffer,
         UInt32 cbToRead,
         out UInt32 cbThatWereRead,
         IntPtr pOverlapped);