cLICK ON show existing raises error

What steps will reproduce the problem?
1.connect to 2 databases click test button to confirm.
2.click on Show Existing Objects checkbox to un-check.
3.error box pops up with message below.

What is the expected output? What do you see instead?

What version of the product are you using? On what operating system?
SQL-DBDiff   v.  0.4.0.0
OS Win 7 enterprise, sp1 

Please provide any additional information below.
Object reference not set to an instance of an object.
   at DBDiff.Front.SchemaTreeView.RebuildSchemaTree()
   at System.Windows.Forms.CheckBox.OnCheckedChanged(EventArgs e)
   at System.Windows.Forms.CheckBox.set_CheckState(CheckState value)
   at System.Windows.Forms.CheckBox.OnClick(EventArgs e)
   at System.Windows.Forms.CheckBox.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

Original issue reported on code.google.com by LaFlamme...@gmail.com on 9 May 2014 at 1:24

TheProjecter / sql-dbdiff

cLICK ON show existing raises error #56