There is a problem with pending tasks (first reported and discussed here: https://groups.google.com/forum/?fromgroups=#!topic/tracksapp/LCM-UAwYJ7s)

This is my scenario:
Get the latest and greatest tracks (2.3devel (2013-03-18 14:16:04 -0400), commit 11c5f988dba7be242de94e2d4c4056230f7d5b14):

git pull origin
bundle install

Edit config/database.yml and enable blank sqlite database:

production:
  adapter: sqlite3
  database: db/tracks-blank.sqlite3.db
  pool: 5
  timeout: 5000

Do the migrate stuff:

bundle exec rake db:migrate RAILS_ENV=production

Ok, done? Start nginx. Tracks is running. I create an admin account - nice.
I create a task "test task one". Nice.
I create a task "test tast two" that depends on "test task one". Bang!! Server error!

A log snipped can be found in the groups post mentioned above.

Reinier posted this first workaround:
Edit file /app/view/todos/_successor.html.erb and insert # in the follwing two lines:

#cache [successor, "successor"] do
...
<% #end %>