Maybe the following errors when starting Banshee could be helpful:

[Info  11:21:54.271] Running Banshee 2.0.0: [Ubuntu Natty (development branch) (linux-gnu, i686) @ 2011-04-18 16:21:33 UTC]
[Info  11:21:56.794] Updating web proxy from GConf
[Info  11:21:56.965] All services are started 2.304885
** (Banshee:5125): DEBUG: SyncDaemon already running, initializing SyncdaemonDaemon object

(Banshee:5125): libsoup-WARNING **: No feature manager for feature of type 'U1RequestChrome'

** (Banshee:5125): WARNING **: Error calling get_info: Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.7/dbus/service.py", line 702, in _message_cb
    retval = candidate_method(self, *args, **keywords)
  File "/usr/lib/pymodules/python2.7/ubuntuone-client/ubuntuone/platform/linux/dbus_interface.py", line 992, in get_info
    return self.syncdaemon_folders.get_info(path)
  File "/usr/lib/pymodules/python2.7/ubuntuone-client/ubuntuone/syncdaemon/interaction_interfaces.py", line 634, in get_info
    mdobj = self.fs.get_by_path(path.encode('utf-8'))
  File "/usr/lib/pymodules/python2.7/ubuntuone-client/ubuntuone/syncdaemon/filesystem_manager.py", line 773, in get_by_path
    mdid = self._idx_path[path]
KeyError: '/home/techtonik/.ubuntuone/Purchased from Ubuntu One'


** (Banshee:5125): CRITICAL **: syncdaemon_folder_info_get_subscribed: assertion `SYNCDAEMON_IS_FOLDER_INFO (finfo)' failed

** (Banshee:5125): WARNING **: Error rescanning Purchased Music: No such file or directory
** (Banshee:5125): DEBUG: Loading the real store page
[Info  11:22:01.577] nereid Client Started
[Info  11:22:01.758] GStreamer version 0.10.32.0, gapless: True, replaygain: False
[Info  11:22:02.239] AppleDeviceSource is ignoring unmounted volume Aeacy
[Info  11:22:02.280] AppleDeviceSource is ignoring unmounted volume New Volume
[Info  11:22:02.336] AppleDeviceSource is ignoring unmounted volume Extra
System.ApplicationException: Could not find org.freedesktop.Avahi
  at Mono.Zeroconf.Providers.AvahiDBus.DBusManager.Initialize () [0x00000] in <filename unknown>:0 
  at Mono.Zeroconf.Providers.AvahiDBus.ZeroconfProvider.Initialize () [0x00000] in <filename unknown>:0 
  at Mono.Zeroconf.Providers.ProviderFactory.GetProviders () [0x00000] in <filename unknown>:0 
[Warn  11:22:02.420] Failed to start DAAP client - System.Exception: No Zeroconf providers could be found or initialized. Necessary daemon may not be running. (in `Mono.Zeroconf')
  at Mono.Zeroconf.Providers.ProviderFactory.GetProviders () [0x00000] in <filename unknown>:0 
  at Mono.Zeroconf.Providers.ProviderFactory.get_DefaultProvider () [0x00000] in <filename unknown>:0 
  at Mono.Zeroconf.Providers.ProviderFactory.get_SelectedProvider () [0x00000] in <filename unknown>:0 
  at Mono.Zeroconf.ServiceBrowser..ctor () [0x00000] in <filename unknown>:0 
  at Daap.ServiceLocator.Start () [0x00000] in <filename unknown>:0 
  at Banshee.Daap.DaapService.ThreadedInitialize () [0x00000] in <filename unknown>:0 
[Warn  11:23:48.119] Asked to invalidate 0+0,0x0 for Hyena.Data.Gui.ColumnCellRating but no CanvasManager!
[Warn  11:23:48.151] Asked to invalidate 0+0,0x0 for Hyena.Data.Gui.ColumnCellRating but no CanvasManager!
...