Redmine

"Tracker","Status","Priority","Subject","Author","Assignee","Category","Target version","Start date","Due date","Estimated time","Private","Exigences","Parent task","Description"
"Development","Normal","In Progress","Subject","some Author","some Assignee","CAT_SAA","G.Ag_V0","2017-02-01","2017-02-10","16.00","No","test","#703","Description"

My redmine is :

Environment:
  Redmine version                3.4.4.stable
  Ruby version                   2.3.1-p112 (2016-04-26) [x86_64-linux-gnu]
  Rails version                  4.2.8
  Environment                    production
  Database adapter               Mysql2
SCM:
  Subversion                     1.9.3
  Git                            2.7.4
  Filesystem                     
Redmine plugins:
  redmine_agile                  1.4.5
  redmine_app__space             1.0.4
  redmine_app_timesheets         1.5.12
  redmine_code_review            0.8.0
  redmine_gitlab_hook            0.1.3
  redmine_highlightjs            1.0.3
  redmine_image_clipboard_paste  3.3.0
  redmine_importer               1.0
  redmine_issues_tree            0.0.10
  redmine_lightbox2              0.4.3
  redmine_omniauth_gitlab        0.0.1
  redmine_spent_time_required    0.0.1
  redmine_user_specific_theme    1.2.0
  redmine_webhook                0.0.2
  redmine_work_time              0.3.4
  scrum                          0.18.0
  timesheet                      0.7.0

After enable it in Admin/Projects/../Modules ，whenever access a menu of the project http://192.168.251.53/projects/rmo2/xxxx , I got the following errlog .

Completed 500 Internal Server Error in 838ms (ActiveRecord: 276.9ms)

ActionView::Template::Error (No route matches {:action=>"index", :controller=>"importer", :project_id=>#<Project id: 52, name: "RMO", description: "RMO_2", homepage: "", is_public: false, parent_id: nil, created_on: "2018-07-23 01:48:34", updated_on: "2018-07-23 01:48:34", identifier: "rmo2", status: 1, lft: 129, rgt: 130, inherit_members: false, default_version_id: nil, default_assigned_to_id: nil, product_backlog_id: nil>}):

Finally , I found that with redmine 3.4.4.stable , the default "import menu" can do that .
Ihe most important thing is that: the value of the "Parent task" is not only integer , it has to contain character # ，such as #816