This error means that you have a corrupt thumbnails database. You'll need to delete the thumbnails database and allow EasyWorship to rebuild it.
  1. Close EasyWorship.
  2. Browse to: c:\users\public\documents\softouch\easyworship\default\v6.1\options\default.ewo\thumbnails and delete the files here.
  3. Open EasyWorship and see if you still get the error.

Note: Your profile folder may be something other than default. The section of the path that looks like this \easyworship\default\v6.1 may be different depending on how your profiles are setup. By default the profile folder will be called "default".