Information
Redmine 2.1.2
Ruby version 1.9.3 (x86_64-linux)
RubyGems version 1.8.24
Rack version 1.4
Rails version 3.2.8
Active Record version 3.2.8
Action Pack version 3.2.8
Active Resource version 3.2.8
Action Mailer version 3.2.8
Active Support version 3.2.8
Environment production
Database adapter mysql2

Database: mysql Ver 14.16 Distrib 5.2.12-MariaDB, for suse-linux-gnu (x86_64) using readline 5.1

Problem
When you copy a project that it doesn't have the wiki module activated, the copy crash. When you copy a project that have the wiki module activated there's no problem.

Code
In app/models/project.rb

def copy_wiki(project)
    # Check that the source project has a wiki first
    unless project.wiki.nil?
      self.wiki ||= Wiki.new
      wiki.attributes = project.wiki.attributes.dup.except("id", "project_id")
      wiki_pages_map = {}
      
      project.wiki.pages.each do |page|
        # Skip pages without content
        next if page.content.nil?
        new_wiki_content = WikiContent.new(page.content.attributes.dup.except("id", "page_id", "updated_on"))
        new_wiki_page = WikiPage.new(page.attributes.dup.except("id", "wiki_id", "created_on", "parent_id"))
        new_wiki_page.content = new_wiki_content
        wiki.pages << new_wiki_page
        wiki_pages_map[page.id] = new_wiki_page
      end
      
      wiki.save
      # Reproduce page hierarchy
      project.wiki.pages.each do |page|
        if page.parent_id && wiki_pages_map[page.id]
          wiki_pages_map[page.id].parent = wiki_pages_map[page.parent_id]
          wiki_pages_map[page.id].save
        end
      end
    end
  end

if you change the code it works correctly

def copy_wiki(project)
    # Check that the source project has a wiki first
    unless project.wiki.nil?
      wiki = Wiki.new
      wiki.attributes = project.wiki.attributes.dup.except("id", "project_id")
      wiki_pages_map = {}
      
      project.wiki.pages.each do |page|
        # Skip pages without content
        next if page.content.nil?
        new_wiki_content = WikiContent.new(page.content.attributes.dup.except("id", "page_id", "updated_on"))
        new_wiki_page = WikiPage.new(page.attributes.dup.except("id", "wiki_id", "created_on", "parent_id"))
        new_wiki_page.content = new_wiki_content
        wiki.pages << new_wiki_page
        wiki_pages_map[page.id] = new_wiki_page
      end
      
      self.wiki = wiki
      wiki.save
      # Reproduce page hierarchy
      project.wiki.pages.each do |page|
        if page.parent_id && wiki_pages_map[page.id]
          wiki_pages_map[page.id].parent = wiki_pages_map[page.parent_id]
          wiki_pages_map[page.id].save
        end
      end
    end
  end

Error log
Started POST "/projects/prova/copy" for 127.0.0.1 at 2013-02-07 11:54:14 +0100
Processing by ProjectsController#copy as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"R/TuuUitlFGsay8MNeshen6pJWpRaquVDl+fyFTVMN8=", "project"=>{"name"=>"testttt", "parent_id"=>"", "description"=>"dasdas", "identifier"=>"testttt", "homepage"=>"", "is_public"=>"0", "custom_field_values"=>{"1"=>"prova"}, "enabled_module_names"=>["issue_tracking", "time_tracking", "news", "documents", "files", "repository", "boards", "calendar", "gantt", "alfresco", "wiki_extensions", ""], "tracker_ids"=>["1", "2", "3", ""]}, "only"=>["members", "versions", "issue_categories", "issues", "queries", "boards", "wiki", ""], "commit"=>"Copia", "id"=>"prova"}
 (0.4ms) SELECT MAX(settings.updated_on) AS max_id FROM settings 
User Load (0.6ms) SELECT users.* FROM users WHERE users.type IN ('User', 'AnonymousUser') AND users.id = 3 AND (users.status = 1) LIMIT 1
Current user: gtanya (id=3)
 (0.1ms) BEGIN
 (0.2ms) SELECT * FROM concurrency_redmine FOR UPDATE
IssueCustomField Load (0.3ms) SELECT custom_fields.* FROM custom_fields WHERE custom_fields.type IN ('IssueCustomField') ORDER BY custom_fields.position
Tracker Load (0.3ms) SELECT trackers.* FROM trackers ORDER BY trackers.position ASC
Project Load (0.8ms) SELECT projects.* FROM projects WHERE (parent_id IS NULL AND status = 1) ORDER BY name
Project Load (0.3ms) SELECT projects.* FROM projects WHERE projects.identifier = 'prova' LIMIT 1
Setting Load (0.3ms) SELECT settings.* FROM settings WHERE settings.name = 'default_projects_public' LIMIT 1
CACHE (0.0ms) SELECT trackers.* FROM trackers ORDER BY trackers.position ASC
Tracker Load (0.3ms) SELECT trackers.* FROM trackers WHERE trackers.id IN (1, 2, 3)
 (0.1ms) DELETE FROM projects_trackers WHERE projects_trackers.project_id IS NULL AND projects_trackers.tracker_id IN (4)
CustomField Load (0.2ms) SELECT custom_fields.* FROM custom_fields WHERE (type = 'ProjectCustomField') ORDER BY position
EnabledModule Exists (0.4ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'issue_tracking' AND enabled_modules.project_id IS NULL) LIMIT 1
EnabledModule Exists (0.3ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'time_tracking' AND enabled_modules.project_id IS NULL) LIMIT 1
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'news' AND enabled_modules.project_id IS NULL) LIMIT 1
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'documents' AND enabled_modules.project_id IS NULL) LIMIT 1
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'files' AND enabled_modules.project_id IS NULL) LIMIT 1
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'repository' AND enabled_modules.project_id IS NULL) LIMIT 1
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'boards' AND enabled_modules.project_id IS NULL) LIMIT 1
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'calendar' AND enabled_modules.project_id IS NULL) LIMIT 1
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'gantt' AND enabled_modules.project_id IS NULL) LIMIT 1
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'alfresco' AND enabled_modules.project_id IS NULL) LIMIT 1
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'wiki_extensions' AND enabled_modules.project_id IS NULL) LIMIT 1
Project Exists (0.2ms) SELECT 1 AS one FROM projects WHERE projects.identifier = BINARY 'testttt' LIMIT 1
Project Load (0.4ms) SELECT projects.* FROM projects ORDER BY rgt desc LIMIT 1 FOR UPDATE
SQL (0.3ms) INSERT INTO projects (created_on, description, homepage, identifier, is_public, lft, name, parent_id, rgt, status, updated_on) VALUES ('2013-02-07 11:54:14', 'dasdas', '', 'testttt', 0, 141, 'testttt', NULL, 142, 1, '2013-02-07 11:54:14')
EnabledModule Exists (0.5ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'issue_tracking' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.8ms) INSERT INTO enabled_modules (name, project_id) VALUES ('issue_tracking', 87)
EnabledModule Exists (0.3ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'time_tracking' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.2ms) INSERT INTO enabled_modules (name, project_id) VALUES ('time_tracking', 87)
EnabledModule Exists (0.3ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'news' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.2ms) INSERT INTO enabled_modules (name, project_id) VALUES ('news', 87)
EnabledModule Exists (0.3ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'documents' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.2ms) INSERT INTO enabled_modules (name, project_id) VALUES ('documents', 87)
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'files' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.1ms) INSERT INTO enabled_modules (name, project_id) VALUES ('files', 87)
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'repository' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.3ms) INSERT INTO enabled_modules (name, project_id) VALUES ('repository', 87)
EnabledModule Exists (0.3ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'boards' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.2ms) INSERT INTO enabled_modules (name, project_id) VALUES ('boards', 87)
EnabledModule Exists (0.3ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'calendar' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.2ms) INSERT INTO enabled_modules (name, project_id) VALUES ('calendar', 87)
EnabledModule Exists (0.3ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'gantt' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.1ms) INSERT INTO enabled_modules (name, project_id) VALUES ('gantt', 87)
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'alfresco' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.2ms) INSERT INTO enabled_modules (name, project_id) VALUES ('alfresco', 87)
EnabledModule Exists (0.2ms) SELECT 1 AS one FROM enabled_modules WHERE (enabled_modules.name = BINARY 'wiki_extensions' AND enabled_modules.project_id = 87) LIMIT 1
SQL (0.1ms) INSERT INTO enabled_modules (name, project_id) VALUES ('wiki_extensions', 87)
 (0.1ms) INSERT INTO projects_trackers (project_id, tracker_id) VALUES (87, 1)
 (0.1ms) INSERT INTO projects_trackers (project_id, tracker_id) VALUES (87, 2)
 (0.1ms) INSERT INTO projects_trackers (project_id, tracker_id) VALUES (87, 3)
SQL (0.2ms) INSERT INTO custom_values (custom_field_id, customized_id, customized_type, value) VALUES (1, 87, 'Project', '')
 (0.3ms) UPDATE custom_values SET value = 'prova' WHERE custom_values.id = 87
Project Load (0.7ms) SELECT projects.* FROM projects WHERE projects.parent_id IS NULL ORDER BY lft
Project Load (0.3ms) SELECT lft, rgt, parent_id FROM projects WHERE projects.id = 25 LIMIT 1 FOR UPDATE
Project Load (0.2ms) SELECT lft, rgt, parent_id FROM projects WHERE projects.id = 87 LIMIT 1 FOR UPDATE
SQL (1.0ms) UPDATE projects SET lft = CASE WHEN lft BETWEEN 123 AND 140 THEN lft + 142 - 140 WHEN lft BETWEEN 141 AND 142 THEN lft + 123 - 141 ELSE lft END, rgt = CASE WHEN rgt BETWEEN 123 AND 140 THEN rgt + 142 - 140 WHEN rgt BETWEEN 141 AND 142 THEN rgt + 123 - 141 ELSE rgt END, parent_id = CASE WHEN id = 87 THEN NULL ELSE parent_id END ORDER BY projects.lft
Project Load (0.3ms) SELECT lft, rgt, parent_id FROM projects WHERE projects.id = 25 LIMIT 1 FOR UPDATE
Project Load (0.3ms) SELECT lft, rgt, parent_id FROM projects WHERE projects.id = 87 LIMIT 1 FOR UPDATE
Project Load (0.3ms) SELECT projects.* FROM projects WHERE projects.id = 87 LIMIT 1
Wiki Load (0.4ms) SELECT wikis.* FROM wikis WHERE wikis.project_id = 1 LIMIT 1
Wiki Load (0.3ms) SELECT wikis.* FROM wikis WHERE wikis.project_id = 87 LIMIT 1
 (0.3ms) UPDATE concurrency_redmine SET id=id+1
 (14.6ms) ROLLBACK
Completed 500 Internal Server Error in 121ms

ActiveRecord::RecordNotSaved (Failed to save the new associated wiki.):
app/models/project.rb:724:in copy_wiki'
app/models/project.rb:675:inblock (2 levels) in copy'
app/models/project.rb:674:in each'
app/models/project.rb:674:inblock in copy'
app/models/project.rb:671:in copy'
app/controllers/projects_controller.rb:128:inblock in copy'
app/models/mailer.rb:364:in with_deliveries'
app/controllers/projects_controller.rb:125:incopy'