[lucid] Missing method AssertInMainThread in assembly

Using Ubuntu 10.04 i386, banshee 1.5.4 from the ppa, and banshee-coverwallpaper 0.1.1-2 from the repositories. Running banshee I get the following and the plug-in has no effect:

nate@nate-desktop:~$ banshee
[Info 14:40:37.712] Running Banshee 1.5.4: [Ubuntu 9.10 (linux-gnu, i486) @ 2010-02-28 00:04:10 UTC]
[Info 14:40:38.143] Starting collection of anonymous usage data

** (Banshee:1756): WARNING **: Missing method AssertInMainThread in assembly /usr/lib/banshee-1/Extensions/Banshee.CoverWallpaper.dll, type Banshee.Base.ThreadAssist

** (Banshee:1756): WARNING **: The class Banshee.Base.ThreadAssist could not be loaded, used in Banshee.CoverWallpaper
[Warn 14:40:39.484] Caught an exception - Could not load type 'Banshee.Base.ThreadAssist' from assembly 'Banshee.CoverWallpaper'. (in `Banshee.Services')
  at Banshee.ServiceStack.ServiceManager.StartExtension (Mono.Addins.TypeExtensionNode node) [0x00000]
[Warn 14:40:39.484] Extension `Banshee.CoverWallpaper.CoverWallpaperService' not started: Could not load type 'Banshee.Base.ThreadAssist' from assembly 'Banshee.CoverWallpaper'.

** (Banshee:1756): WARNING **: Missing method AssertInMainThread in assembly /usr/lib/banshee-1/Extensions/Banshee.CoverWallpaper.dll, type Banshee.Base.ThreadAssist

** (Banshee:1756): WARNING **: The class Banshee.Base.ThreadAssist could not be loaded, used in Banshee.CoverWallpaper
[Warn 14:40:39.485] Caught an exception - Could not load type 'Banshee.Base.ThreadAssist' from assembly 'Banshee.CoverWallpaper'. (in `Banshee.Services')
  at Banshee.ServiceStack.ServiceManager.StartExtension (Mono.Addins.TypeExtensionNode node) [0x00000]
[Warn 14:40:39.485] Extension `Banshee.CoverWallpaper.CoverWallpaperService' not started: Could not load type 'Banshee.Base.ThreadAssist' from assembly 'Banshee.CoverWallpaper'.
[Info 14:40:39.488] All services are started 1.472722s
[Info 14:40:40.359] nereid Client Started
nate@nate-desktop:~$ banshee-1
[Info 14:42:42.043] Running Banshee 1.5.4: [Ubuntu 9.10 (linux-gnu, i486) @ 2010-02-28 00:04:10 UTC]
[Info 14:42:42.471] Starting collection of anonymous usage data

** (Banshee:1822): WARNING **: Missing method AssertInMainThread in assembly /usr/lib/banshee-1/Extensions/Banshee.CoverWallpaper.dll, type Banshee.Base.ThreadAssist

** (Banshee:1822): WARNING **: The class Banshee.Base.ThreadAssist could not be loaded, used in Banshee.CoverWallpaper
[Warn 14:42:43.845] Caught an exception - Could not load type 'Banshee.Base.ThreadAssist' from assembly 'Banshee.CoverWallpaper'. (in `Banshee.Services')
  at Banshee.ServiceStack.ServiceManager.StartExtension (Mono.Addins.TypeExtensionNode node) [0x00000]
[Warn 14:42:43.845] Extension `Banshee.CoverWallpaper.CoverWallpaperService' not started: Could not load type 'Banshee.Base.ThreadAssist' from assembly 'Banshee.CoverWallpaper'.

** (Banshee:1822): WARNING **: Missing method AssertInMainThread in assembly /usr/lib/banshee-1/Extensions/Banshee.CoverWallpaper.dll, type Banshee.Base.ThreadAssist

** (Banshee:1822): WARNING **: The class Banshee.Base.ThreadAssist could not be loaded, used in Banshee.CoverWallpaper
[Warn 14:42:43.847] Caught an exception - Could not load type 'Banshee.Base.ThreadAssist' from assembly 'Banshee.CoverWallpaper'. (in `Banshee.Services')
  at Banshee.ServiceStack.ServiceManager.StartExtension (Mono.Addins.TypeExtensionNode node) [0x00000]
[Warn 14:42:43.847] Extension `Banshee.CoverWallpaper.CoverWallpaperService' not started: Could not load type 'Banshee.Base.ThreadAssist' from assembly 'Banshee.CoverWallpaper'.
[Info 14:42:43.849] All services are started 1.506904s
[Info 14:42:44.724] nereid Client Started
[Info 14:42:51.645] Uncached artwork size 175 requested