To reproduce:

1) Add audiobook to source
2) open audiobook in audiobook source
3) mark files and drag to source
4) release when the playlist creation appears

The same crash will now also occur when a user clicks the newly created invalid upon restarting Banshee.

[1 Warn  14:32:50.717] Nereid.SourceContents.TitleWidget is no longer used (from {0}) - Lydbøger
[1 Debug 14:32:51.357] Creating Pango.Layout, configuring Cairo.Context
Exception in Gtk# callback delegate
  Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception.
System.ArgumentNullException: Argument cannot be null.
Parameter name: stream
  at System.IO.StreamReader.Initialize (System.IO.Stream stream, System.Text.Encoding encoding, Boolean detectEncodingFromByteOrderMarks, Int32 bufferSize) [0x00000] in <filename unknown>:0 
  at System.IO.StreamReader..ctor (System.IO.Stream stream, System.Text.Encoding encoding, Boolean detectEncodingFromByteOrderMarks, Int32 bufferSize) [0x00000] in <filename unknown>:0 
  at System.IO.StreamReader..ctor (System.IO.Stream stream) [0x00000] in <filename unknown>:0 
  at (wrapper remoting-invoke-with-check) System.IO.StreamReader:.ctor (System.IO.Stream)
  at Hyena.Gui.ActionManager.AddUiFromFile (System.String ui_file, System.Reflection.Assembly assembly) [0x00006] in /home/david/Projekter/banshee/src/Hyena/Hyena.Gui/Hyena.Gui/ActionManager.cs:173 
  at Banshee.Gui.InterfaceActionService.OnActiveSourceChangedGui () [0x000dd] in /home/david/Projekter/banshee/src/Core/Banshee.ThickClient/Banshee.Gui/InterfaceActionService.cs:111 
  at Hyena.ThreadAssist.ProxyToMain (Hyena.InvokeHandler handler) [0x0001a] in /home/david/Projekter/banshee/src/Hyena/Hyena/Hyena/ThreadAssist.cs:103 
  at Banshee.Gui.InterfaceActionService.OnActiveSourceChanged (Banshee.Sources.SourceEventArgs args) [0x00000] in /home/david/Projekter/banshee/src/Core/Banshee.ThickClient/Banshee.Gui/InterfaceActionService.cs:80 
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at (wrapper delegate-invoke) Banshee.Sources.SourceEventHandler:invoke_void__this___SourceEventArgs (Banshee.Sources.SourceEventArgs)
  at Banshee.Sources.SourceManager.SetActiveSource (Banshee.Sources.Source source, Boolean notify) [0x00083] in /home/david/Projekter/banshee/src/Core/Banshee.Services/Banshee.Sources/SourceManager.cs:364 
  at Banshee.Sources.SourceManager.SetActiveSource (Banshee.Sources.Source source) [0x00000] in /home/david/Projekter/banshee/src/Core/Banshee.Services/Banshee.Sources/SourceManager.cs:336 
  at Banshee.Sources.Gui.SourceView.OnButtonPressEvent (Gdk.EventButton press) [0x0014f] in /home/david/Projekter/banshee/src/Core/Banshee.ThickClient/Banshee.Sources.Gui/SourceView.cs:270 
  at Gtk.Widget.buttonpressevent_cb (IntPtr widget, IntPtr evnt) [0x00000] in <filename unknown>:0 
   at GLib.ExceptionManager.RaiseUnhandledException(System.Exception e, Boolean is_terminal)
   at Gtk.Widget.buttonpressevent_cb(IntPtr widget, IntPtr evnt)
   at Gtk.Application.gtk_main()
   at Gtk.Application.Run()
   at Banshee.Gui.GtkBaseClient.Run() in /home/david/Projekter/banshee/src/Core/Banshee.ThickClient/Banshee.Gui/GtkBaseClient.cs:line 205
   at Banshee.Gui.GtkBaseClient.Startup() in /home/david/Projekter/banshee/src/Core/Banshee.ThickClient/Banshee.Gui/GtkBaseClient.cs:line 82
   at Hyena.Gui.CleanRoomStartup.Startup(Hyena.Gui.StartupInvocationHandler startup) in /home/david/Projekter/banshee/src/Hyena/Hyena.Gui/Hyena.Gui/CleanRoomStartup.cs:line 54
   at Banshee.Gui.GtkBaseClient.Startup() in /home/david/Projekter/banshee/src/Core/Banshee.ThickClient/Banshee.Gui/GtkBaseClient.cs:line 77
   at Banshee.Gui.GtkBaseClient.Startup(System.String[] args) in /home/david/Projekter/banshee/src/Core/Banshee.ThickClient/Banshee.Gui/GtkBaseClient.cs:line 67
   at Nereid.Client.Main(System.String[] args) in /home/david/Projekter/banshee/src/Clients/Nereid/Nereid/Client.cs:line 54
   at System.AppDomain.ExecuteAssembly(System.Reflection.Assembly , System.String[] )
   at System.AppDomain.ExecuteAssemblyInternal(System.Reflection.Assembly a, System.String[] args)
   at System.AppDomain.ExecuteAssembly(System.String assemblyFile, System.Security.Policy.Evidence assemblySecurity, System.String[] args)
   at System.AppDomain.ExecuteAssembly(System.String assemblyFile)
   at Booter.Booter.BootClient(System.String clientName) in /home/david/Projekter/banshee/src/Clients/Booter/Booter/Entry.cs:line 112
   at Booter.Booter.Main() in /home/david/Projekter/banshee/src/Clients/Booter/Booter/Entry.cs:line 105