Redmine

Hi all,
i facing problem to upgrade redmine 0.9 to 2.1 version .i am not able to see issues page .it gives below error .
i also made change in data base . i am attaching dump file it will help to solve problem

Started GET "/projects/aprmar201213it/issues" for 127.0.0.1 at 2012-10-24 23:45:
32 +0530
Processing by IssuesController#index as HTML
Parameters: {"project_id"=>"aprmar201213it"}
Current user: admin (id=1)
Rendered queries/_filters.html.erb (0.0ms)
Rendered queries/_columns.html.erb (0.0ms)
Rendered issues/_list.html.erb (0.0ms)
Rendered issues/index.html.erb within layouts/base (93.8ms)
Completed 500 Internal Server Error in 156ms

ActionView::Template::Error (undefined method `-' for nil:NilClass):
24: </td>
25: </tr>
26: <% previous_group = group >
27: < end >
28: <tr id="issue-<= issue.id >" class="hascontextmenu <= cycle('odd',
'even') > <= issue.css_classes > <= level > 0 ? "idnt idnt-#{level}" : nil %

">

29: <td class="checkbox hide-when-print"><%= check_box_tag("ids[]", issu
e.id, false, :id => nil) ></td>
30: <td class="id"><= link_to issue.id, issue_path(issue) %></td>
lib/plugins/awesome_nested_set/lib/awesome_nested_set/awesome_nested_set.rb:24
7:in `leaf?'
app/models/issue.rb:862:in `css_classes'
app/views/issues/_list.html.erb:27:in `block (2 levels) in app_views_issues_
list_html_erb__616546365_23108448'
app/helpers/issues_helper.rb:29:in `block in issue_list'
app/helpers/issues_helper.rb:25:in `each'
app/helpers/issues_helper.rb:25:in `issue_list'
app/views/issues/_list.html.erb:15:in `block in app_views_issues_list_html_e
rb__616546365_23108448'
app/views/issues/_list.html.erb:1:in `_app_views_issues__list_html_erb__616546
365_23108448'
app/views/issues/index.html.erb:58:in `_app_views_issues_index_html_erb___2168
78069_36751596'
app/controllers/issues_controller.rb:82:in `block (2 levels) in index'
app/controllers/issues_controller.rb:81:in `index'