Redmine

When I'm in an issue and click on the bottom on the pdf link, I get a 500 error.
Here are the logs :

Processing IssuesController#show to pdf (for 192.168.140.5 at 2011-01-19 16:23:09) [GET] Parameters: {"format"=>"pdf", "action"=>"show", "id"=>"51", "controller"=>"issues"}

NoMethodError (private method `gsub' called for nil:NilClass): lib/redmine/export/pdf.rb:258:in `issue_to_pdf' app/controllers/issues_controller.rb:119:in `show' app/controllers/issues_controller.rb:115:in `show'

Rendering /home/redmine/redmine-1.1.0/public/500.html (500 Internal Server Error)

I'm on a debian Lenny 64 bits. Redmine 1.1.0. Here is the gem list :

gem list

LOCAL GEMS ***
actionmailer (1.0.1)
actionpack (1.9.1, 1.0.1)
activemodel (3.0.3)
activerecord (3.0.3)
activesupport (3.0.3, 1.1.1, 1.0.1)
arel (2.0.6)
builder (2.1.2)
cgi_multipart_eof_fix (2.5.0)
daemons (1.1.0, 1.0.1)
fastthread (1.0.1)
gem_plugin (0.2.3)
gruff (0.3.6)
holidays (1.0.0)
i18n (0.4.2)
icalendar (1.0.1)
mongrel (1.0.1)
prawn (0.8.4)
prawn-core (0.8.4)
prawn-layout (0.8.4)
prawn-security (0.8.4)
rack (1.0.1)
tzinfo (0.3.23)

Is someone can help me?
Thank you.