0.5.0: "F-Spot Encountered a Fatal Error"

Hello,

I tried upgrading to the recently released F-Spot 0.5.0, and got the
following errors.  When launching F-Spot it pops up an alert dialog
titled "F-Spot Encountered a Fatal Error:  Extension node not found in
path: /FSpot/Sidebar".  When I click the Error Details link, I get the
following information:

        An unhandled exception was thrown: Extension node not found in
        path: /FSpot/Sidebar

          at Mono.Addins.ExtensionContext.AddExtensionNodeHandler
        (System.String path, Mono.Addins.ExtensionNodeEventHandler
        handler) [0x00000] 
          at Mono.Addins.AddinManager.AddExtensionNodeHandler
        (System.String path, Mono.Addins.ExtensionNodeEventHandler
        handler) [0x00000] 
          at MainWindow..ctor (.Db db) [0x00000] 
          at FSpot.Core.get_MainWindow () [0x00000] 
          at FSpot.Core.Organize () [0x00000] 
          at FSpot.Driver.Main (System.String[] args) [0x00000] 
        .NET Version: 2.0.50727.42

        Assembly Version Information:

        pango-sharp (2.12.0.0)
        SemWeb (0.7.1.0)
        glade-sharp (2.12.0.0)
        FSpot.Widgets (0.0.0.0)
        FSpot.JobScheduler (0.0.0.0)