[4 Debug 06:38:09.434] Invalid thumbnail, reloading: file:///home/paul/Photos/2010/09/22/CSC_6942.JPG
[4 Debug 06:38:09.435] Failed loading image for thumbnailing: file:///home/paul/Photos/2010/09/22/CSC_6942.JPG
[4 Warn  06:38:09.441] Caught an exception - System.Exception: Unsupported image: file:///home/paul/Photos/2010/09/22/CSC_6942.JPG (in `f-spot')
  at FSpot.Imaging.ImageFile.Create (Hyena.SafeUri uri) [0x0004c] in /home/paul/src/f-spot/src/Clients/MainApp/FSpot.Imaging/ImageFile.cs:171 
  at FSpot.Driver.<Main>m__5F (Hyena.SafeUri uri) [0x00000] in /home/paul/src/f-spot/src/Clients/MainApp/FSpot/main.cs:181 
  at FSpot.Utils.XdgThumbnailSpec.CreateFrom (Hyena.SafeUri uri, Hyena.SafeUri thumb_uri, ThumbnailSize size, FSpot.Utils.PixbufLoader loader) [0x00016] in /home/paul/src/f-spot/src/Core/FSpot.Utils/FSpot.Utils/XdgThumbnailSpec.cs:97 
[1 Debug 06:39:13.779] open uri = file:///home/paul/Photos/2010/09/22/DSC_6835.JPG
Exception in Gtk# callback delegate
  Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception.
GLib.GException: Error stating file '/home/paul/Photos/2010/09/22/CSC_6942.JPG': No such file or directory
  at GLib.FileAdapter.QueryInfo (System.String attributes, FileQueryInfoFlags flags, GLib.Cancellable cancellable) [0x00000] in <filename unknown>:0 
  at FSpot.Utils.Metadata.Parse (Hyena.SafeUri uri) [0x0000c] in /home/paul/src/f-spot/src/Core/FSpot.Utils/FSpot.Utils/Metadata.cs:43 
  at FSpot.Widgets.InfoBox.Update () [0x0004c] in /home/paul/src/f-spot/src/Clients/MainApp/FSpot.Widgets/InfoBox.cs:507 
  at FSpot.Utils.DelayedOperation.HandleOperation () [0x0000d] in /home/paul/src/f-spot/src/Core/FSpot.Utils/FSpot.Utils/DelayedOperation.cs:57 
  at GLib.Idle+IdleProxy.Handler () [0x00000] in <filename unknown>:0 
   at GLib.ExceptionManager.RaiseUnhandledException(System.Exception e, Boolean is_terminal)
   at GLib.Idle+IdleProxy.Handler()
   at Gtk.Application.gtk_main()
   at Gtk.Application.Run()
   at FSpot.Driver.Startup() in /home/paul/src/f-spot/src/Clients/MainApp/FSpot/main.cs:line 390
   at Hyena.Gui.CleanRoomStartup.Startup(Hyena.Gui.StartupInvocationHandler startup) in /home/paul/src/f-spot/lib/Hyena/Hyena.Gui/Hyena.Gui/CleanRoomStartup.cs:line 54
   at FSpot.Driver.Main(System.String[] args) in /home/paul/src/f-spot/src/Clients/MainApp/FSpot/main.cs:line 308

I would expect to be able to remove this from the catalog out of F-Spot without having to go manually into the SQLite database. As far as I remember this works, if the thumbnail is already created, but I'd have to check. The reason is, again, in InfoBox.cs, but is not fixed by the the patch submitted for bug #636694.