I'm assuming again... that 'MenuItem4' is part of 'ContextMenu1', what happens if, after you change the value, you reassign the menu contents to the 'NotifyIcon1.ContextMenu' ?

VB Code:
  1. Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
  2.    NotifyIcon1.ContextMenu = ContextMenu1
  3.    Me.ContextMenu = ContextMenu1
  4. End Sub
  5.  
  6. Private Sub ContextMenu1_Popup(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ContextMenu1.Popup
  7.    MenuItem4.Text = TextBox1.Text
  8.    NotifyIcon1.ContextMenu = ContextMenu1
  9. End Sub

I'm thinking that because the two objects are technically separate as they're not on the same 'form' they don't automatically both 'see' changes to 'Contextmenu1'... just a thought.