Redmine

更新一个问题的时间，页面就报如下错误，这个错误怎么解决？
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-->production.log 错误如下：

Processing IssuesController#update (for 10.1.0.175 at 2014-06-18 21:04:52) [PUT]
Parameters: {"time_entry"=>{"comments"=>"", "activity_id"=>"", "hours"=>""}, "commit"=>"提交", "notes"=>"", "action"=>"update", "_method"=>"put", "authenti
city_token"=>"22OQOv/6xq3OwpoU6zYizE1iNL7xpHxwpN+uqo9kGIk=", "id"=>"51635", "issue"=>{"start_date"=>"2014-06-17", "custom_field_values"=>{"52"=>"ALL", "41"=>
"", "5"=>"OS 6.0"}, "estimated_hours"=>"", "parent_issue_id"=>"51622", "priority_id"=>"7", "is_private"=>"0", "lock_version"=>"0", "fixed_version_id"=>"", "a
ssigned_to_id"=>"282", "subject"=>"OS6_编辑模式- 批量移入图标至文件夹及从文件夹批量移出图标 功能", "category_id"=>"", "tracker_id"=>"4", "due_date"=>"2014-0
6-18", "status_id"=>"1", "description"=>"1.批量移动图标至文件夹\r\n2.从文件夹批量移出图标\r\n3.新建文件夹"}, "controller"=>"issues", "attachments"=>{"1"=>{"d
escription"=>""}, "screenshot"=>{"name"=>"screenshot", "content"=>"", "description"=>""}}}

ArgumentError (comparison of Date with nil failed):
app/models/issue.rb:606:in `save_issue_with_child_records'
app/models/issue.rb:588:in `save_issue_with_child_records'
app/controllers/issues_controller.rb:174:in `update'
thin (1.5.0) lib/thin/connection.rb:81:in `pre_process'
thin (1.5.0) lib/thin/connection.rb:79:in `catch'
thin (1.5.0) lib/thin/connection.rb:79:in `pre_process'
thin (1.5.0) lib/thin/connection.rb:54:in `process'
thin (1.5.0) lib/thin/connection.rb:39:in `receive_data'
D:/redmine/Ruby187/lib/ruby/gems/1.8/gems/eventmachine-1.0.0-x86-mingw32/lib/eventmachine.rb:187:in `run_machine'
D:/redmine/Ruby187/lib/ruby/gems/1.8/gems/eventmachine-1.0.0-x86-mingw32/lib/eventmachine.rb:187:in `run'
thin (1.5.0) lib/thin/backends/base.rb:63:in `start'
thin (1.5.0) lib/thin/server.rb:159:in `start'
thin (1.5.0) lib/thin/controllers/controller.rb:86:in `start'
thin (1.5.0) lib/thin/runner.rb:187:in `send'
thin (1.5.0) lib/thin/runner.rb:187:in `run_command'
thin (1.5.0) lib/thin/runner.rb:152:in `run!'
thin (1.5.0) bin/thin:6
D:/redmine/Ruby187/bin/thin:19:in `load'
D:/redmine/Ruby187/bin/thin:19

Rendering D:/redmine/redmine/public/500.html (500 Internal Server Error)