「heroku run...」で何かを実行すると、次のエラーが発生します。
/Users/tony/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/exceptions.rb:48:in `<class:GemNotFoundException>': undefined method `errors' for nil:NilClass (NoMethodError)
from /Users/tony/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/exceptions.rb:40:in `<top (required)>'
from <internal:lib/rubygems/custom_require>:29:in `require'
from <internal:lib/rubygems/custom_require>:29:in `require'
from /Users/tony/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems.rb:1235:in `<top (required)>'
from <internal:lib/rubygems/custom_require>:29:in `require'
from <internal:lib/rubygems/custom_require>:29:in `require'
from /Users/tony/.rvm/gems/ruby-1.9.2-p290/bin/heroku:9:in `<main>'
以前は正常に動作していました。
何か助けはありますか?