Redmine

Hi guys,

I tried to upgrade from 2.3.1 to 2.4.2, everything seemed to have worked smoothly (DB upgrade was also fine) and Redmine worked as expected till I tried to create a new issue.
This is what I've got in my production.log:

Started GET "/searchissues?project_id=7&issue_id=&query=Test" for IP at Tue Jan 07 17:03:12 +0100 2014
Processing by SearchIssuesController#index as */*
Parameters: {"project_id"=>"7", "issue_id"=>"", "query"=>"Test"}
Current user: user (id=ID)
Completed 200 OK in 36.4ms (Views: 0.6ms | ActiveRecord: 5.1ms)
Started POST "/projects/ID2/issues" for IP 07 17:03:42 +0100 2014
Processing by IssuesController#create as HTML
Parameters: {"commit"=>"Anlegen", "issue"=>{"description"=>"Test", "parent_issue_id"=>"", "is_private"=>"0", "estimated_hours"=>"1", "subject"=>"Test", "assigned_to_id"=>"5", "done_ratio"=>"0", "priority_id"=>"2", "start_date"=>"2014-01-07", "due_date"=>"2014-01-07", "tag_list"=>"", "tracker_id"=>"3", "status_id"=>"1"}, "authenticity_token"=>"TOKEN", "utf8"=>"✓", "project_id"=>"ID2", "new_checklist"=>""}
Current user: georg.b (id=5)
Rendered mailer/_issue.text.erb (201.2ms)
Rendered mailer/issue_add.text.erb within layouts/mailer (208.2ms)
Completed 500 Internal Server Error in 693.9ms

ArgumentError (wrong number of arguments (1 for 3)):
app/models/mailer.rb:422:in `initialize'
app/models/mailer.rb:445:in `method_missing'
app/models/issue_observer.rb:20:in `after_create'
app/models/issue.rb:165:in `create_or_update'
app/controllers/issues_controller.rb:146:in `create'

Right now, I rolled back to 2.3.1 and can continue working.
Anybody else got similar issues with 2.4.2?

PS: System info
Environment:
Redmine version 2.3.1.stable
Ruby version 1.8.7-p352 (2011-06-30) [x86_64-linux]
Rails version 3.2.13
Environment production
Database adapter Mysql2
Redmine plugins:
clipboard_image_paste 1.7
progressive_projects_list 0.4.0
redmine_didyoumean 1.2.0
redmine_issue_checklist 2.0.5
redmine_issue_detailed_tabs_time 0.0.7
redmine_tags 2.0.1-dev

CentOS 6.4