Ruby (Rack) application could not be started

A source file that the application requires, is missing.
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  • A required library may not installed. Please install all libraries that this application requires.
Further information about the error may have been written to the application's log file. Please check it in order to analyse the problem.
Error message:
no such file to load -- dm-migrations
Exception class:
LoadError
Application root:
/var/www/sites/df4.us
Backtrace:
# File Line Location
0 /usr/lib/ruby/1.8/rubygems/custom_require.rb 31 in `gem_original_require'
1 /usr/lib/ruby/1.8/rubygems/custom_require.rb 31 in `require'
2 ./dfshorty.rb 5
3 /usr/lib/ruby/1.8/rubygems/custom_require.rb 31 in `gem_original_require'
4 /usr/lib/ruby/1.8/rubygems/custom_require.rb 31 in `require'
5 config.ru 1
6 /var/lib/gems/1.8/gems/rack-1.2.1/lib/rack/builder.rb 46 in `instance_eval'
7 /var/lib/gems/1.8/gems/rack-1.2.1/lib/rack/builder.rb 46 in `initialize'
8 config.ru 1 in `new'
9 config.ru 1