testing
 I found the problem.
 Hey... this InvokeRequired variable is interesting....!!
 Anyway I manage to single thread the code in my data

 --
 If you're in a war, instead of throwing a hand grenade at the enemy, throw one of those small pumpkins. Maybe it'll make everyone think how stupid war is, and while they are thinking, you can throw a real grenade at them.
 Jack Handey.
   "David Levine" <noSpam12dlevineNNTP2@wi.rr.com> wrote in message news:%238As3ujpFHA.420@TK2MSFTNGP09.phx.gbl...
   If the method Invalidate accesses some controls and it is getting invoked on a thread other then the one the controls were created on (which is what may  be happening by using BeginInvoke ), then you need to invoke a method to do the updating on the original thread. You can easily check by checking the control's field InvokeRequired

   For example,

   if ( this.someControl.InvokeRequired )
       this.someControl.Invoke( new MyDelegate( MyDelegatedMethod),args );

     "Lloyd Dupont" <ld@NewsAccount.galador.net> wrote in message news:upQcGljpFHA.3156@TK2MSFTNGP10.phx.gbl...
     I have a program which use multithread.
     Inadvertently dare I say, as they are not my threads but those of a FileSystemWatcher.

     Anyway some method get called on my GUI.
     I rewrite the code in such a way that it should only be to a funtion like that:
     void HTreeChanged(object sender, TreeEventArgs e)
     {
         if(base.Created)
             BeginInvoke(new Action(Invalidate));
     }
     however there is, apparently, another method call on an other thread.
     the problem is I have no idea which one and VS.NET popup a message box saying:
     System.InvalidOperationException was unhandled
     Message: Cross-thread operation not valid: Control '' accessed from a thread other than the thread it was created on.

     but even though I looked at all the active thread's stack I have no idea which method is throwing..

     what can I do?