Userform - validate controls data when a listbox on the form

Hi guys,
I have an issue with userform and validation of data (not on an excel sheet here)
On the userform, Userform1, I have:
- a listbox called lbx
- a textbox called txt
- a command button called cmd
I fill the listbox during _Initialize and check the data in txt_BeforeUpdate(Cancel) and cancels the update if not valid data.
Now, if the data is not valid, i warn the user with a message and i'd like to give him a chance to change the enter data.
When running, if you enter data and click another item in the listbox, the message is displayed, but the listbox updates to the new selection preventing the user to re-entrer the data for his previous selection. I have posted my code below.

I have tried the txt_Exit event too, but to no avail.
Any idea would be greatly appreciated.

Thanks,
Sebastien

Here is the code:
'-------------------------------------------------------------------------------
Option Explicit

Private StoredValue() As Double

Private CodeMode As Boolean 'to cancel events when they are
                            ' triggered from my code and not
                            ' from the user

'Filling the listbox first
Private Sub UserForm_Initialize()
   Dim i As Long, ttl As Long
   
   CodeMode = True  'prevent events
   
   With lbx
      .AddItem "aaa"
      .AddItem "bbb"
   End With
   
   ttl = lbx.ListCount
   ReDim StoredValue(0 To ttl - 1)
   For i = 0 To ttl - 1: StoredValue(i) = i: Next
   
   CodeMode = False
End Sub

'When listbox is clicked, show the corresponding
' value in the textbox txt
Private Sub lbx_Click()
   'Cancel event if CodeMode
   If CodeMode Then Exit Sub
   
   txt = StoredValue(lbx.ListIndex)
   
End Sub

'Now the user can edit the textbox
'Validation: check data when the usere leaves the textbox
'       it has to be a number else prevent the update
Private Sub txt_BeforeUpdate(ByVal Cancel As MSForms.ReturnBoolean)
   Dim d As Double
   
   CodeMode = True 'cancel events
   
   'Validation
   On Error Resume Next
   d = CDbl(txt)
   If Err <> 0 Then
      MsgBox "you must enter a number"
      Cancel = True 'Cancel the update of the textbox
   Else
      StoredValue(lbx.ListIndex) = CDbl(txt)
   End If
   
   CodeMode = False
End Sub
'----------------------------------------------------------------