Redmine

Good morning to all,

I have a redmine 2.4.2 installation (using the bitnami stack). My problem is when users are trying to create a subproject, where upon "Create" they get an Error 500. If they logout and login again, the subproject is created though. In production.log I'm getting these:

=====
Started POST "/redmine/projects" for 10.0.0.10 at 2014-04-27 10:45:24 +0300
Processing by ProjectsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"Fsh260U+n9dgL5lrOfmAVOnpNgAsMdBk6/+3mXzQwpQ=", "project"=>{"name"=>"Dokimi_01", "section_id"=>"4", "description"=>"", "identifier"=>"my-test-pq", "homepage"=>"", "is_public"=>"1", "parent_id"=>"27", "inherit_members"=>"1", "enabled_module_names"=>["issue_tracking", "time_tracking", "documents", "files", "calendar", "gantt", "charts", "daily_status", "dashboard", "work_time", "scrum2b", "stuff_to_do", ""], "tracker_ids"=>["1", "2", "3", "4", ""]}, "commit"=>"Create"}
Current user: admin (id=1)
Completed 500 Internal Server Error in 344.9ms

NoMethodError (undefined method `session_id' for #<Project:0x007fc1c568c9f8>):
lib/plugins/awesome_nested_set/lib/awesome_nested_set/awesome_nested_set.rb:491:in `move_to'
lib/plugins/awesome_nested_set/lib/awesome_nested_set/awesome_nested_set.rb:361:in `move_to_child_of'
app/models/project.rb:1038:in `set_or_update_position_under'
app/models/project.rb:409:in `set_parent!'
app/models/project.rb:391:in `set_allowed_parent!'
app/controllers/projects_controller.rb:84:in `create'

=====

Has anyone come up to this before?

Thanks for any help!
Nick