Threads and ...CriticalRegion

Hi,

I have the following code that uses beginCriticalRegion and
EndCriticalRegion

Imports System.Threading
Public Class Form1
Shared Sub SimpleWorks(ByVal o As Object)
Dim info As person = CType(o, person)

Thread.BeginCriticalRegion()
Thread.Sleep(100)
MsgBox(Thread.CurrentThread.ManagedThreadId & " " & info.Name)
Thread.EndCriticalRegion()
End Sub
Dim operation As New ParameterizedThreadStart(AddressOf
SimpleWorks)

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click

Dim theThreads1 As New Thread(operation)
Dim P1 As New person("mimi", " rogers")
theThreads1.Start(P1)

Dim P2 As New person("Ina", "Forrester")

Dim theThreads2 As New Thread(operation)
theThreads2.Start(P2)
'HERE IS NOT WORKING
theThreads2.Abort()

Dim P3 As New person("Dave", "Simpson")
Dim theThreads3 As New Thread(operation)
theThreads3.Start(P3)

End Sub
End Class

I find that theThreads2 is still aborted before displaying the message:
Msgbox.......

Can somebody enlighten me.

Thank you,

Carly