Redmine

When I migrate from my Trac 0.12 database using sqlite3. I encounter this error :

Not knowing much about ruby I have some problems finding where it comes from

www-data@myserver:~/public/ruby/redmine-1.0.3$ rake redmine:migrate_from_trac RAILS_ENV="production" --trace
(in /home/www-data/public/ruby/redmine-1.0.3)

• Invoke redmine:migrate_from_trac (first_time)
• Invoke environment (first_time)
• Execute environment
• Execute redmine:migrate_from_trac

WARNING: a new project will be added to Redmine during this process.
Are you sure you want to continue ? [y/N] y

Trac directory []: /home/www-data/public/python/trac/myproject/
Trac database adapter (sqlite, sqlite3, mysql, postgresql) [sqlite3]:
Trac database encoding [UTF-8]:
Target project identifier []: myproject

Migrating components..
Migrating milestones....
Migrating custom fields
Migrating tickets................
Migrating wiki...........................................................................................................rake aborted!

no implicit conversion to float from nil
/home/www-data/public/ruby/redmine-1.0.3/vendor/rails/activesupport/lib/active_support/core_ext/time/calculations.rb:277:in `minus_without_duration'
/home/www-data/public/ruby/redmine-1.0.3/vendor/rails/activesupport/lib/active_support/core_ext/time/calculations.rb:277:in `minus_without_coercion'
/home/www-data/public/ruby/redmine-1.0.3/vendor/rails/activesupport/lib/active_support/core_ext/time/calculations.rb:286:in `-'
/home/www-data/public/ruby/redmine-1.0.3/lib/tasks/migrate_from_trac.rake:79:in `fake'
/home/www-data/public/ruby/redmine-1.0.3/lib/tasks/migrate_from_trac.rake:547:in `migrate'
/home/www-data/public/ruby/redmine-1.0.3/vendor/rails/activerecord/lib/active_record/associations/association_collection.rb:369:in `method_missing'
/home/www-data/public/ruby/redmine-1.0.3/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:215:in `method_missing'
/home/www-data/public/ruby/redmine-1.0.3/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:215:in `each'
/home/www-data/public/ruby/redmine-1.0.3/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:215:in `send'
/home/www-data/public/ruby/redmine-1.0.3/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:215:in `method_missing'
/home/www-data/public/ruby/redmine-1.0.3/vendor/rails/activerecord/lib/active_record/associations/association_collection.rb:369:in `method_missing'
/home/www-data/public/ruby/redmine-1.0.3/lib/tasks/migrate_from_trac.rake:545:in `migrate'
/home/www-data/public/ruby/redmine-1.0.3/lib/tasks/migrate_from_trac.rake:758
/usr/lib/ruby/1.8/rake.rb:636:in `call'
/usr/lib/ruby/1.8/rake.rb:636:in `execute'
/usr/lib/ruby/1.8/rake.rb:631:in `each'
/usr/lib/ruby/1.8/rake.rb:631:in `execute'
/usr/lib/ruby/1.8/rake.rb:597:in `invoke_with_call_chain'
/usr/lib/ruby/1.8/monitor.rb:242:in `synchronize'
/usr/lib/ruby/1.8/rake.rb:590:in `invoke_with_call_chain'
/usr/lib/ruby/1.8/rake.rb:583:in `invoke'
/usr/lib/ruby/1.8/rake.rb:2051:in `invoke_task'
/usr/lib/ruby/1.8/rake.rb:2029:in `top_level'
/usr/lib/ruby/1.8/rake.rb:2029:in `each'
/usr/lib/ruby/1.8/rake.rb:2029:in `top_level'
/usr/lib/ruby/1.8/rake.rb:2068:in `standard_exception_handling'
/usr/lib/ruby/1.8/rake.rb:2023:in `top_level'
/usr/lib/ruby/1.8/rake.rb:2001:in `run'
/usr/lib/ruby/1.8/rake.rb:2068:in `standard_exception_handling'
/usr/lib/ruby/1.8/rake.rb:1998:in `run'
/usr/bin/rake:28