我正在使用Ruby on Rails中的应用程序，我改变了我的Rails和Rake版本。 rails server不再有效：
~/sample_app/config.ru:4:in `block in <main>': uninitialized constant SampleApp (NameError)
from /var/lib/gems/1.9.1/gems/rack-1.2.8/lib/rack/builder.rb:46:in `instance_eval'
from /var/lib/gems/1.9.1/gems/rack-1.2.8/lib/rack/builder.rb:46:in `initialize'
from /home/sara/Documents/M1/s8/web avancé/projet/sample_app/config.ru:1:in `new'
from /home/sara/Documents/M1/s8/web avancé/projet/sample_app/config.ru:1:in `<main>'
from /var/lib/gems/1.9.1/gems/rack-1.2.8/lib/rack/builder.rb:35:in `eval'
from /var/lib/gems/1.9.1/gems/rack-1.2.8/lib/rack/builder.rb:35:in `parse_file'
from /var/lib/gems/1.9.1/gems/rack-1.2.8/lib/rack/server.rb:162:in `app'
from /var/lib/gems/1.9.1/gems/rack-1.2.8/lib/rack/server.rb:253:in `wrapped_app'
from /var/lib/gems/1.9.1/gems/rack-1.2.8/lib/rack/server.rb:204:in `start'
from /var/lib/gems/1.9.1/gems/railties-3.0.7/lib/rails/commands/server.rb:65:in `start'
from /var/lib/gems/1.9.1/gems/railties-3.0.7/lib/rails/commands.rb:30:in `block in <top (required)>'
from /var/lib/gems/1.9.1/gems/railties-3.0.7/lib/rails/commands.rb:27:in `tap'
from /var/lib/gems/1.9.1/gems/railties-3.0.7/lib/rails/commands.rb:27:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'