HideCaret() Windows API function doesn't work properly

I want to hide the caret in the RichTextBox control and do that with the win api function HideCaret(),but it doesn't work.The cursor is still visible and blinking.Where i should call the function.I tried in the Enter event of the control but doesn't work again.As far as i know i should call the HideCaret() when the RichTextBox gets the focus.Is that right?
Here is the code:

[DllImport("User32.dll")]
static extern Boolean HideCaret(System.IntPtr hWnd);

private void richTextBox1_Enter(object sender, EventArgs e)
{
HideCaret(richTextBox1.Handle);
}

I tried some possibilities ( etc.) but with no success.