500 Encoding Error Page can't be loaded because of an encoding error.

Hi When I commit my changes to my server, it's done OK, but when I want to see it from Web UI, it gives above error. this problem happens for some of my commits and most of them are OK, I searched and got this issues: https://gitlab.com/gitlab-org/gitlab-ce/issues/710 https://github.com/gitlabhq/gitlabhq/issues/8115

My gitlab Info is:

System information
System:         Ubuntu 12.04
Current User:   git
Using RVM:      no
Ruby Version:   2.1.2p95
Gem Version:    2.2.2
Bundler Version:1.6.4
Rake Version:   10.4.2
Sidekiq Version:3.3.0

GitLab information
Version:        7.11.4
Revision:       b725318
Directory:      /home/git/gitlab
DB Adapter:     mysql2
URL:            https://git.example.com
HTTP Clone URL: https://git.example.com/some-project.git
SSH Clone URL:  git@git.example.com:some-project.git
Using LDAP:     no
Using Omniauth: no

GitLab Shell
Version:        2.6.3
Repositories:   /home/git/repositories/
Hooks:          /home/git/gitlab-shell/hooks/
Git:            /usr/bin/git

Nginx Log:

- - [14/Jun/2015:12:43:04 +0430] "GET /user/project/commit/deee454033f503d15017bb80bd7946ea44cc0531 HTTP/1.1" 500 4448 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.2357.124 Safari/537.36"

production.log:

Started GET "/user/project/commit/deee454033f503d15017bb80bd7946ea44cc0531" for xx.xx.xx.xx at 2015-06-14 12:14:40 +0430
Processing by Projects::CommitController#show as HTML
  Parameters: {"namespace_id"=>"user", "project_id"=>"project", "id"=>"deee454033f503d15017bb80bd7946ea44cc0531"}

Encoding::CompatibilityError (incompatible character encodings: UTF-8 and ASCII-8BIT):
  app/views/projects/diffs/_file.html.haml:45:in `_app_views_projects_diffs__file_html_haml___3306403215734696238_70092753570780'
  app/views/projects/diffs/_diffs.html.haml:15:in `block in _app_views_projects_diffs__diffs_html_haml___815215432062336350_70092673923100'
  app/views/projects/diffs/_diffs.html.haml:14:in `each'
  app/views/projects/diffs/_diffs.html.haml:14:in `each_with_index'
  app/views/projects/diffs/_diffs.html.haml:14:in `_app_views_projects_diffs__diffs_html_haml___815215432062336350_70092673923100'
  app/views/projects/commit/show.html.haml:3:in `_app_views_projects_commit_show_html_haml__2863232771886072554_70092653874260'
  app/controllers/projects/commit_controller.rb:25:in `show'

Completed 500 Internal Server Error in 1969ms (Views: 47.5ms | ActiveRecord: 3.5ms)

would you please help me to solve this problem. thanks