Can't start timer from Visio event handler

[Eli]

I'm developing a Visual Basic .Net app that interacts with
Visio 2002. I have an event handler in VB to handle the
Visio "SelectionChanged" event. This event handler is
called when the event is fired. However, the handler
quits when it tries to enable my timer.

Private Sub oVisioApp_SelectionChanged(ByVal Window As
Microsoft.Office.Interop.Visio.Window) Handles
oVisioApp.SelectionChanged

Debug.WriteLine("Timer starting...") ' Prints correctly
Me.Timer1.Enabled = True ' Funtion exits, timer off
Debug.WriteLine("Timer on") ' Doesn't print!

End Sub

The first debug output is printed correctly, but the
function quits when it tries to enable the timer.

I've tried the same code in other Visio event handlers and
got the same results.

In addition to not being able to start the timer, I also
cannot dynamically add a textbox control to a panel from
this event handler. It fails in the same way that it
fails when trying to start the timer.

Me.Panel1.Controls.AddRange(New
System.Windows.Forms.Control() {tb})

Where tb is a new textbox.

Any ideas appreciated.
-Eli