Redmine

Hi,

suddenly I get errors when Redmine tries to send an email. Nothing has changed in the configuration since years. So this is complete strange and I can not see the course.

This is the error log I see in the logs:

Started PUT "/issues/2721" for xx.xx.xx.xx at 2015-04-01 19:21:03 +0200
Processing by IssuesController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"xxxxx", "issue"=>{"is_private"=>"0", "project_id"=>"75", "tracker_id"=>"4", "subject"=>"Errormeldungen der Saunasteuerung", "description"=>"Implementieren der Errormeldungen der Saunasteuerung", "status_id"=>"2", "priority_id"=>"4", "assigned_to_id"=>"8", "fixed_version_id"=>"", "parent_issue_id"=>"", "start_date"=>"2015-04-01", "due_date"=>"", "estimated_hours"=>"", "done_ratio"=>"0", "custom_field_values"=>{"1"=>"", "2"=>"0"}, "notes"=>"", "private_notes"=>"0", "lock_version"=>"1"}, "time_entry"=>{"hours"=>"", "activity_id"=>"", "comments"=>""}, "last_journal_id"=>"4720", "commit"=>"OK", "id"=>"2721"}
  Current user: xxxxxxxxx (id=8)
  Rendered mailer/_issue.text.erb (5.9ms)
  Rendered mailer/issue_edit.text.erb within layouts/mailer (10.2ms)
  Rendered mailer/_issue.html.erb (1.9ms)
  Rendered mailer/issue_edit.html.erb within layouts/mailer (5.1ms)
Email delivery error: can't convert true into String
Redirected to http://server.homecomfort.at:3000/issues/2721
Completed 302 Found in 333.7ms (ActiveRecord: 15.0ms)

As you can see, I get the error: Email delivery error: can't convert true into String

Does anybody know where I should look? Where does this error really come from? Could it be something in the database?
The database is MySQL and works perfect. There is plenty of space on the hard disc.

This is the installed Redmine:

Environment:
  Redmine version                2.4.1.stable
  Ruby version                   1.9.3-p448 (2013-06-27) [i686-linux]
  Rails version                  3.2.15
  Environment                    production
  Database adapter               Mysql2
SCM:
  Subversion                     1.6.12
  Cvs                            1.12.13
  Git                            1.7.2.5
  Filesystem                     
Redmine plugins:
  a_common_libs                  0.0.1
  redmine_dashboard              2.2.2
  redmine_login_audit            0.1.3
  redmine_pipeline_plugin        1.0.0
  redmine_scm                    0.4.3
  redmine_todos                  2.0.5
  redmine_tweaks                 0.4.5
  timelog_on_issue_page          0.0.1

I know that this is an older version, but I don't want to upgrade if not really necessary.

A.T.