Here's what the log says:

# Logfile created on Fri Jul 18 17:30:24 -0400 2008


ActiveRecord::StatementInvalid (Mysql::Error: #HY000You can't specify target table 't' for update in FROM clause: update cards t set references_expired=1 where (t.tag_id in (select id from cards tx  where tx.id = '53' and tx.trash='f'    ))):
    /var/lib/gems/1.8/gems/activerecord-2.0.2/lib/active_record/connection_adapters/abstract_adapter.rb:150:in `log'
    /var/lib/gems/1.8/gems/activerecord-2.0.2/lib/active_record/connection_adapters/mysql_adapter.rb:281:in `execute'
    /app/models/card/templating.rb:148:in `expire_templatee_references'
    /app/models/card/references.rb:19:in `update_references_on_update'

(more in changes history)