Hi Jack,

Thanks for your post!

Since you are using Elapsed event, I am assuming that you are using
System.Timers.Timer class. This timer will fire the Elapsed event in
another thread instead of the main thread. While your .Net Winform controls
are all STA, which are not thread-safe, they can not be invoked by another
thread, so this error message is generated. This is by design.

In .Net winform area, the correct way to deal with cross-thread calling is
marshal the method calling with Control.Invoke method. Sample code like
this:

Public Delegate Sub FormCloseEventHandler()
Private Sub Timer1_Elapsed(ByVal sender As Object, ByVal e As
System.Timers.ElapsedEventArgs) Handles Timer1.Elapsed
       If Form1.InvokeRequired Then
           Form1.Invoke(New FormCloseEventHandler(AddressOf Form1.Close))
       Else
           Form1.Close()
       End If
   End Sub

Alternately, you may set Timer1.SynchronizingObject property to the
control/form. This is the buildin synchronization method provided by
System.Timers.Timer class.

Finally, please refer to the article below for more information regarding
difference between various timer class in .Net:
"Comparing the Timer Classes in the .NET Framework Class Library"
http://msdn.microsoft.com/msdnmag/issues/04/02/TimersinNET/

Hope this helps.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
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Jack,

Setting the SynchronizingObject property of System.Timers.Timer is the
best option IMO.  Though, you could use System.Windows.Forms.Timer as
well.

Brian