Ubuntu – Rhythmbox and Banshee do not start anymore

I searched a little and tried your topic Banshee isn't starting anymore, but I still had no success yet.
So I will explain my problem shortly and then post the error-messages:

Both players worked fine until Rhythmbox suddenly crashed and didn't start any more. So I tried Banshee (they are both installed on my system) and it crashed after a few seconds while scanning for new media and doesn't start any more either.
Both players can be started from other users, for example as sudo or at the guest-account. So there is possibly something wrong with the user, but I don't know what.
So, thanks for your help!

Here are the error-messages:

Rhythmbox

(rhythmbox:8836): Gtk-CRITICAL **: gtk_style_provider_get_style_property: assertion `g_type_is_a (gtk_widget_path_get_object_type (path), pspec->owner_type)' failed

(rhythmbox:8836): Gtk-CRITICAL **: gtk_style_provider_get_style_property: assertion `g_type_is_a (gtk_widget_path_get_object_type (path), pspec->owner_type)' failed

(rhythmbox:8836): Gtk-CRITICAL **: gtk_style_provider_get_style_property: assertion `g_type_is_a (gtk_widget_path_get_object_type (path), pspec->owner_type)' failed

(rhythmbox:8836): Gtk-CRITICAL **: gtk_style_provider_get_style_property: assertion `g_type_is_a (gtk_widget_path_get_object_type (path), pspec->owner_type)' failed

(rhythmbox:8836): Gtk-CRITICAL **: gtk_style_provider_get_style_property: assertion `g_type_is_a (gtk_widget_path_get_object_type (path), pspec->owner_type)' failed
/usr/lib/python2.7/dist-packages/gobject/constants.py:24: Warning: g_boxed_type_register_static: assertion `g_type_from_name (name) == 0' failed
  import gobject._gobject
TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases
**
ERROR:/build/buildd/pygobject-3.0.0/gi/_gobject/pygobject.c:929:pygobject_new_full: assertion failed: (tp != NULL)
Aborted

Banshee

[Info  02:59:35.413] Running Banshee 2.2.0: [Ubuntu oneiric (development branch) (linux-gnu, x86_64) @ 2011-09-23 04:47:58 UTC]
Exception in Gtk# callback delegate
  Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception.
System.ArgumentException: Value does not fall within the expected range.
  at Hyena.Gui.Canvas.Rect.set_Width (Double value) [0x00000] in <filename unknown>:0 
  at Hyena.Gui.Canvas.Rect.op_Explicit (Rectangle rect) [0x00000] in <filename unknown>:0 
  at Hyena.Data.Gui.ListView`1[Banshee.Collection.AlbumInfo].OnSizeAllocated (Rectangle allocation) [0x00000] in <filename unknown>:0 
  at Gtk.Widget.sizeallocated_cb (IntPtr widget, IntPtr allocation) [0x00000] in <filename unknown>:0 
   at GLib.ExceptionManager.RaiseUnhandledException(System.Exception e, Boolean is_terminal)
   at Gtk.Widget.sizeallocated_cb(IntPtr widget, IntPtr allocation)
   at Gtk.Widget.gtksharp_widget_base_show(IntPtr )
   at Gtk.Widget.OnShown()
   at Nereid.PlayerInterface.OnShown()
   at Gtk.Widget.shown_cb(IntPtr widget)
   at Gtk.Widget.gtk_widget_show(IntPtr )
   at Gtk.Widget.Show()
   at Banshee.Gui.BaseClientWindow.InitialShowPresent()
   at Nereid.PlayerInterface.Initialize()
   at Banshee.Gui.BaseClientWindow.InitializeWindow()
   at Banshee.Gui.BaseClientWindow..ctor(System.String title, System.String configNameSpace, Int32 defaultWidth, Int32 defaultHeight)
   at Nereid.PlayerInterface..ctor()
   at System.Reflection.MonoCMethod.InternalInvoke(System.Reflection.MonoCMethod , System.Object , System.Object[] , System.Exception ByRef )
   at System.Reflection.MonoCMethod.Invoke(System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
   at System.Reflection.MonoCMethod.Invoke(BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
   at System.Reflection.ConstructorInfo.Invoke(System.Object[] parameters)
   at System.Activator.CreateInstance(System.Type type, Boolean nonPublic)
   at System.Activator.CreateInstance(System.Type type)
   at Banshee.ServiceStack.ServiceManager.RegisterService(System.Type type)
   at Banshee.ServiceStack.ServiceManager.Run()
   at Banshee.ServiceStack.Application.Run()
   at Banshee.Gui.GtkBaseClient.Initialize(Boolean registerCommonServices)
   at Banshee.Gui.GtkBaseClient..ctor(Boolean initializeDefault, System.String defaultIconName)
   at Banshee.Gui.GtkBaseClient..ctor()
   at Nereid.Client..ctor()
   at System.Reflection.MonoCMethod.InternalInvoke(System.Reflection.MonoCMethod , System.Object , System.Object[] , System.Exception ByRef )
   at System.Reflection.MonoCMethod.Invoke(System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
   at System.Reflection.MonoCMethod.Invoke(BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
   at System.Reflection.ConstructorInfo.Invoke(System.Object[] parameters)
   at System.Activator.CreateInstance(System.Type type, Boolean nonPublic)
   at System.Activator.CreateInstance(System.Type type)
   at Banshee.Gui.GtkBaseClient.Startup()
   at Hyena.Gui.CleanRoomStartup.Startup(Hyena.Gui.StartupInvocationHandler startup)
   at Banshee.Gui.GtkBaseClient.Startup()
   at Banshee.Gui.GtkBaseClient.Startup(System.String[] args)
   at Nereid.Client.Main(System.String[] args)
   at System.AppDomain.ExecuteAssembly(System.AppDomain , 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)
   at Booter.Booter.Main()