How do I allow CTRL-V (Paste) on a Winforms Textbox?

Check to see if you have a menu on the form with a shortcut for Ctrl-V.

The following code should help:

private void textBox1_KeyUp(object sender, KeyEventArgs e) {
  if (e.KeyData == Keys.V && e.Modifiers == Keys.Control)
    (sender as Textbox).Paste();
}