Steps to reproduce:
1. start banshee 0.11.5
2. click on Edit -> Plugins -> Podcasting checkbox



Stack trace:
Debug: [1/25/2007 5:38:49 PM] (Loading audio profiles) - /usr/local/share/banshee/audio-profiles
Debug: [1/25/2007 5:38:50 PM] (Default player engine) - GStreamer 0.10
Debug: [1/25/2007 5:38:50 PM] (Audio CD Core Initialized) - 
Debug: [1/25/2007 5:38:50 PM] (Testing device for DAP support) - /org/freedesktop/Hal/devices/volume_uuid_06F496FCF496ED65
Debug: [1/25/2007 5:38:50 PM] (DAP has not been added) - /org/freedesktop/Hal/devices/volume_uuid_06F496FCF496ED65
Debug: [1/25/2007 5:38:50 PM] (Testing device for DAP support) - /org/freedesktop/Hal/devices/volume_uuid_aab517c7_3f77_4296_b1db_50e54982097b
Debug: [1/25/2007 5:38:50 PM] (DAP has not been added) - /org/freedesktop/Hal/devices/volume_uuid_aab517c7_3f77_4296_b1db_50e54982097b
Debug: [1/25/2007 5:38:50 PM] (Renaming column PlaylistID in SmartPlaylists) - 
Debug: [1/25/2007 5:38:50 PM] (Renaming column PlaylistID in SmartPlaylistEntries) - 
Object reference not set to an instance of an object
System.NullReferenceException: Object reference not set to an instance of an object
at Banshee.Plugins.Podcast.UI.PodcastSource.GetSelectedFeed () <0x0001c>
at Banshee.Plugins.Podcast.UI.PodcastSource.OnFeedViewSelectionChanged (object,System.EventArgs) <0x00013>
at (wrapper delegate-invoke) System.MulticastDelegate.invoke_void_object_EventArgs (object,System.EventArgs) <0x00041>
at GLib.Signal.voidObjectCallback (intptr,intptr) <0x00093>
at (wrapper native-to-managed) GLib.Signal.voidObjectCallback (intptr,intptr) <0x00035>
in (unmanaged) 0xb6630b28
at (wrapper managed-to-native) Gtk.TreeSelection.gtk_tree_selection_select_iter (intptr,Gtk.TreeIter&) <0x00004>
at Gtk.TreeSelection.SelectIter (Gtk.TreeIter) <0x0001e>
at Banshee.Plugins.Podcast.UI.PodcastFeedView.SelectFeed (Banshee.Plugins.Podcast.PodcastFeedInfo) <0x00055>
at Banshee.Plugins.Podcast.UI.PodcastFeedView.OnModelPodcastFeedAdded (object,Banshee.Plugins.Podcast.PodcastFeedEventArgs) <0x00026>
at (wrapper delegate-invoke) System.MulticastDelegate.invoke_void_object_PodcastFeedEventArgs (object,Banshee.Plugins.Podcast.PodcastFeedEventArgs) <0x00041>
at Banshee.Plugins.Podcast.UI.PodcastFeedModel.EmitPodcastFeedAdded (Banshee.Plugins.Podcast.PodcastFeedInfo) <0x00040>
at Banshee.Plugins.Podcast.UI.PodcastFeedModel.AddPodcastFeed (Banshee.Plugins.Podcast.PodcastFeedInfo,bool) <0x000d9>
at Banshee.Plugins.Podcast.UI.PodcastFeedModel.AddPodcastFeed (Banshee.Plugins.Podcast.PodcastFeedInfo) <0x0000f>
at (wrapper delegate-invoke) System.MulticastDelegate.invoke_void_PodcastFeedInfo (Banshee.Plugins.Podcast.PodcastFeedInfo) <0x0003b>
at Banshee.Plugins.Podcast.UI.PodcastFeedModel.PumpQueue (System.Collections.ArrayList,Banshee.Plugins.Podcast.UI.PodcastFeedModel/SingleFeedAction,Banshee.Plugins.Podcast.UI.PodcastFeedModel/MultipleFeedAction) <0x00102>
at Banshee.Plugins.Podcast.UI.PodcastFeedModel.PumpAddQueue () <0x00076>
at (wrapper delegate-invoke) System.MulticastDelegate.invoke_bool () <0x00037>
at IdleProxy.Handler () <0x0002a>
at (wrapper native-to-managed) IdleProxy.Handler () <0x00036>
in (unmanaged) 0xb7e81aa0
at (wrapper managed-to-native) Gtk.Dialog.gtk_dialog_run (intptr) <0x00004>
at Gtk.Dialog.Run () <0x00024>
at Banshee.Plugins.PluginCore.ShowPluginDialog () <0x0002c>
at Banshee.PlayerUI.OnPluginsAction (object,System.EventArgs) <0x00007>
at (wrapper delegate-invoke) System.MulticastDelegate.invoke_void_object_EventArgs (object,System.EventArgs) <0x00041>
at GLib.Signal.voidObjectCallback (intptr,intptr) <0x00093>
at (wrapper native-to-managed) GLib.Signal.voidObjectCallback (intptr,intptr) <0x00035>
in (unmanaged) 0xb6630b28
at (wrapper managed-to-native) Gtk.Application.gtk_main () <0x00004>
at Gtk.Application.Run () <0x00007>
at Banshee.BansheeEntry.Startup (string[]) <0x006a3>
at (wrapper delegate-invoke) System.MulticastDelegate.invoke_void_string[] (string[]) <0x00048>
at Banshee.Gui.CleanRoomStartup.Startup (Banshee.Gui.CleanRoomStartup/StartupInvocationHandler,string[]) <0x000ae>


=================================================================
Got a SIGSEGV while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries 
used by your application.
=================================================================

Stacktrace:

  at (wrapper managed-to-native) Gtk.Container.gtk_container_set_border_width (intptr,uint) <0x00004>
  at (wrapper managed-to-native) Gtk.Container.gtk_container_set_border_width (intptr,uint) <0xffffffff>
  at Gtk.Container.set_BorderWidth (uint) <0x0001d>
  at Banshee.Gui.Dialogs.ExceptionDialog..ctor (System.Exception) <0x0012d>
  at Banshee.Gui.CleanRoomStartup.Startup (Banshee.Gui.CleanRoomStartup/StartupInvocationHandler,string[]) <0x000f7>
  at Banshee.BansheeEntry.Main (string[]) <0x00038>
  at (wrapper runtime-invoke) System.Object.runtime_invoke_void_string[] (object,intptr,intptr,intptr) <0xffffffff>

Native stacktrace:

        banshee(mono_handle_native_sigsegv+0xde) [0x815644e]
        banshee [0x8122c88]
        [0xffffe440]
        /usr/lib/libgobject-2.0.so.0(g_signal_emit+0x29) [0xb6635279]
        /usr/lib/libgobject-2.0.so.0 [0xb6627d11]
        /usr/lib/libgobject-2.0.so.0 [0xb662456f]
        /usr/lib/libgobject-2.0.so.0(g_object_notify+0x2b2) [0xb6628852]
        /usr/lib/libgtk-x11-2.0.so.0(gtk_container_set_border_width+0x61) [0xb69830c1]
        [0xb14d3e07]
        [0xb14d3dbe]
        [0xb2cf374e]
        [0xb7934990]
        [0xb7933c69]
        [0xb7933a73]
        banshee(mono_runtime_exec_main+0x62) [0x80996b2]
        banshee(mono_runtime_run_main+0x1b9) [0x8099999]
        banshee(mono_main+0xe47) [0x805d477]
        banshee [0x805c122]
        /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xdc) [0xb7ce08cc]
        banshee [0x805c071]
Aborted (core dumped)


Other information:
this was the second (first successful) time loading banshee since switching from an older (0.11.3) version. The first time banshee hung on splash screen, and then the window manager stopped responding, X was restarted.