Redmine

I have redmine 1.0.1 and am trying to install redmine_backlogs plugin. The db:migrate etc worked fully. However after restarting redmine, when I click on the backlogs or dashboards tab, I get 500 error. Here is my environment and stack trace from production.log file of redmine.

Environment:

Ubuntu 8.04.1
ruby 1.8.7 patch 303
abstract (1.0.0)
actionmailer (2.3.5)
actionpack (2.3.5)
activerecord (2.3.5)
activeresource (2.3.5)
activesupport (2.3.5)
arel (2.0.7)
builder (2.1.2)
bundler (1.0.9)
calendar (1.11.4)
daemons (1.1.0)
erubis (2.6.6)
eventmachine (0.12.10)
gchart (1.0.0)
holidays (1.0.0)
i18n (0.4.1)
icalendar (1.1.5)
json (1.5.1)
mysql (2.8.1)
prawn (0.8.4)
prawn-core (0.8.4)
prawn-layout (0.8.4)
prawn-security (0.8.4)
rack (1.0.1)
rails (2.3.5)
rake (0.8.7)
subexec (0.0.4)
thin (1.2.7)

I am getting the following error in the production.log while trying to access the backlog/dashboard after installation. I am running nginx as front-end and thin as the rails server.

NoMethodError (undefined method `days' for #<Version:0xb6766234>):
vendor/plugins/redmine_backlogs/app/models/sprint.rb:23:in `initialize'
vendor/plugins/redmine_sprints/app/controllers/sprints_controller.rb:217:in `new'
vendor/plugins/redmine_sprints/app/controllers/sprints_controller.rb:217:in `burndown'
thin (1.2.7) lib/thin/connection.rb:76:in `pre_process'
thin (1.2.7) lib/thin/connection.rb:74:in `catch'
thin (1.2.7) lib/thin/connection.rb:74:in `pre_process'
thin (1.2.7) lib/thin/connection.rb:57:in `process'
thin (1.2.7) lib/thin/connection.rb:42:in `receive_data'
eventmachine (0.12.10) lib/eventmachine.rb:256:in `run_machine'
eventmachine (0.12.10) lib/eventmachine.rb:256:in `run'
thin (1.2.7) lib/thin/backends/base.rb:57:in `start'
thin (1.2.7) lib/thin/server.rb:156:in `start'
thin (1.2.7) lib/thin/controllers/controller.rb:80:in `start'
thin (1.2.7) lib/thin/runner.rb:177:in `send'
thin (1.2.7) lib/thin/runner.rb:177:in `run_command'
thin (1.2.7) lib/thin/runner.rb:143:in `run!'
thin (1.2.7) bin/thin:6
/usr/local/bin/thin:19:in `load'
/usr/local/bin/thin:19

Any help would be much appreciated. Please ask me for any additional info that you may need. Thanks.