关联github repository出错 400 请求报错

求助：使用Octopress与github搭建博客时， 

安装好Octopress后，

rake git@github.com:username/username.github.com.git

rake aborted!
Don't know how to build task 'git@github.com:username/username.github.com.git'
c:/Ruby192/lib/ruby/1.9.1/rake.rb:1720:in `[]'
c:/Ruby192/lib/ruby/1.9.1/rake.rb:2040:in `invoke_task'
c:/Ruby192/lib/ruby/1.9.1/rake.rb:2019:in `block (2 levels) in top_level'
c:/Ruby192/lib/ruby/1.9.1/rake.rb:2019:in `each'
c:/Ruby192/lib/ruby/1.9.1/rake.rb:2019:in `block in top_level'
c:/Ruby192/lib/ruby/1.9.1/rake.rb:2058:in `standard_exception_handling'
c:/Ruby192/lib/ruby/1.9.1/rake.rb:2013:in `top_level'
c:/Ruby192/lib/ruby/1.9.1/rake.rb:1992:in `run'
c:/Ruby192/bin/rake:31:in `<main>'

  请指教