Rvm: 无法删除 ruby​​，想重新安装特定版本，因为无法运行、测试应用程序、错误

我无法使用 ruby​​ 2.1.0 删除 ruby​​、重新安装 ruby​​、启动或测试特定的 rails 项目。
如何删除和安装新的 ruby​​？

错误示例：
1.

$ rails s
/Users/user/.rvm/gems/ruby-2.1.0/bin/rails:23:in `load': cannot load such file -- /Users/user/.rvm/gems/ruby-2.1.0/gems/railties-4.1.1/bin/rails (LoadError)
    from /Users/user/.rvm/gems/ruby-2.1.0/bin/rails:23:in `<main>'
    from /Users/user/.rvm/gems/ruby-2.1.0/bin/ruby_executable_hooks:15:in `eval'
    from /Users/user/.rvm/gems/ruby-2.1.0/bin/ruby_executable_hooks:15:in `<main>'

2.

$ rvm remove ruby-2.1.0
ruby-2.1.0 - #removing src/ruby-2.1.0..
ruby-2.1.0 - #removing rubies/ruby-2.1.0......................................
Error running '__rvm_rm_rf /Users/user/.rvm/rubies/ruby-2.1.0',
showing last 15 lines of /Users/user/.rvm/log/1405545940_ruby-2.1.0/remove.rubies.log
rm: /Users/user/.rvm/rubies/ruby-2.1.0/lib/ruby/gems/2.1.0/gems/nokogiri-1.6.2.1/test: Permission denied
rm: /Users/user/.rvm/rubies/ruby-2.1.0/lib/ruby/gems/2.1.0/gems/nokogiri-1.6.2.1/test_all: Permission denied
rm: /Users/user/.rvm/rubies/ruby-2.1.0/lib/ruby/gems/2.1.0/gems/nokogiri-1.6.2.1/Y_U_NO_GEMSPEC.md: Permission denied
rm: /Users/user/.rvm/rubies/ruby-2.1.0/lib/ruby/gems/2.1.0/gems/nokogiri-1.6.2.1: Directory not empty
rm: /Users/user/.rvm/rubies/ruby-2.1.0/lib/ruby/gems/2.1.0/gems: Directory not empty
rm: /Users/user/.rvm/rubies/ruby-2.1.0/lib/ruby/gems/2.1.0: Directory not empty
rm: /Users/user/.rvm/rubies/ruby-2.1.0/lib/ruby/gems: Directory not empty
rm: /Users/user/.rvm/rubies/ruby-2.1.0/lib/ruby: Directory not empty
rm: /Users/user/.rvm/rubies/ruby-2.1.0/lib: Directory not empty
rm: /Users/user/.rvm/rubies/ruby-2.1.0: Directory not empty
++ typeset ret=1
++ rvm_debug '__rvm_rm_rf error removing target dir '\''/Users/user/.rvm/rubies/ruby-2.1.0'\''.'
++ ((  0  ))
++ return 0
++ return 1

移除 nokogiri 会影响其他 gem

其他修复尝试：
Unknown ruby string (do not know how to handle): ruby-2.1.0.