I just experienced an exception thrown by the vertical scrollbar opening a worksheet (collection was modified; enumeration operation may not execute);
I cannot reproduce so may be some threading issue...
Errore message (got it again)
System.InvalidOperationException: L'insieme è stato modificato. L'operazione di enumerazione potrebbe non essere eseguita.
in System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
in System.Collections.Generic.List`1.Enumerator.MoveNextRare()
in System.Collections.Generic.List`1.Enumerator.MoveNext()
in SMath.Control.RichScrollBar.DrawBookmarks(Graphics g)
in SMath.Control.RichScrollBar.OnPaint(PaintEventArgs e)
in System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer, Boolean disposeEventArgs)
in System.Windows.Forms.Control.WmPaint(Message& m)
in System.Windows.Forms.Control.WndProc(Message& m)
in System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
in System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)