错误描述：
RuntimeError - [Xcodeproj] Unknown object version.
/Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.23.1/lib/xcodeproj/project.rb:206:in `initialize_from_file‘
/Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.23.1/lib/xcodeproj/project.rb:91:in `open‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/installer/analyzer.rb:676:in `block (2 levels) in compute_target_platforms‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/installer/analyzer.rb:673:in `each‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/installer/analyzer.rb:673:in `block in compute_target_platforms‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/user_interface.rb:49:in `section‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/installer/analyzer.rb:672:in `compute_target_platforms‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/installer/analyzer.rb:52:in `analyze‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/installer.rb:189:in `analyze‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/installer.rb:111:in `block in resolve_dependencies‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/user_interface.rb:49:in `section‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/installer.rb:110:in `resolve_dependencies‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/installer.rb:90:in `install!‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/command/project.rb:71:in `run_install_with_update‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/command/project.rb:101:in `run‘
/Library/Ruby/Gems/2.0.0/gems/claide-0.8.1/lib/claide/command.rb:312:in `run‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/lib/cocoapods/command.rb:46:in `run‘
/Library/Ruby/Gems/2.0.0/gems/cocoapods-0.36.4/bin/pod:44:in `<top (required)>‘
/usr/bin/pod:23:in `load‘
/usr/bin/pod:23:in `<main>‘
前奏：
#需要管理员权限
gem update --system
gem install rubygems-update
update_rubygems
高潮：
sudo rm -fr ~/.cocoapods/repos/master
pod setup
测试：
pod update
参考：
http://linglong117.blog.163.com/blog/static/27714547201421225958/
解决[Xcodeproj] Unknown object version错误
原文：http://www.cnblogs.com/ht-927/p/4483352.html