Someone

System.InvalidCastException: Cannot cast from source type to destination type.
  at Npgsql.NpgsqlDataReader.GetInt32 (Int32 i) [0x00010] in /var/tmp/portage/mono-1.2.2.1/work/mono-1.2.2.1/mcs/class/Npgsql/Npgsql/NpgsqlDataReader.cs:587 
  at Mono.Data.Sql.NpgsqlDbProvider.GetUsers () [0x00000] 
  at MonoQuery.UsersNodeBuilder.BuildChildNodes (ITreeBuilder builder, MonoQuery.UsersNode node) [0x00000] 
  at MonoQuery.UsersNodeBuilder.BuildChildNodes (ITreeBuilder builder, System.Object dataObject) [0x00000] 
  at MonoDevelop.Ide.Gui.Pads.TreeViewPad+TreeBuilder.CreateChildren (MonoDevelop.Ide.Gui.Pads.NodeBuilder[] chain, System.Object dataObject) [0x00000] 
  at MonoDevelop.Ide.Gui.Pads.TreeViewPad+TreeBuilder.FillNode () [0x00000] 
  at MonoDevelop.Ide.Gui.Pads.TreeViewPad.OnTestExpandRow (System.Object sender, Gtk.TestExpandRowArgs args) [0x00000] 
  at (wrapper delegate-invoke) System.MulticastDelegate:invoke_void_object_TestExpandRowArgs (object,Gtk.TestExpandRowArgs)
  at Gtk.TreeView.TestExpandRowSignalCallback (IntPtr arg0, Gtk.TreeIter& arg1, IntPtr arg2, IntPtr gch) [0x00000] 
  at (wrapper native-to-managed) Gtk.TreeView:TestExpandRowSignalCallback (intptr,Gtk.TreeIter&,intptr,intptr)
  at <0x00000> <unknown method>
  at (wrapper managed-to-native) Gtk.Application:gtk_main ()
  at Gtk.Application.Run () [0x00000] 
  at MonoDevelop.Ide.Gui.IdeApp.Run () [0x00000] 
  at MonoDevelop.Ide.Gui.IdeStartup.Run (System.String[] args) [0x00000] 
  at MonoDevelop.Core.AddIns.AddInService.StartApplication (System.String addinId, System.String[] parameters) [0x00000]