Heroku deploys "Invalid RUBY_VERSION specified", worked yesterday

I was able to deploy on the hero yesterday just fine. We are in a cedar stack with rails 3.2. When I deploy it, it gives me the following:

$ git push -f heroku-ab-staging  tmp-heroku-deploy-gochez_heroku_test-2012-05-08-10-43-39:master
Counting objects: 222, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (162/162), done.
Writing objects: 100% (191/191), 112.28 KiB, done.
Total 191 (delta 45), reused 13 (delta 0)

-----> Heroku receiving push
-----> Ruby/Rails app detected
 !
 !     Invalid RUBY_VERSION specified: fatal:-Not-a-git-repository:-'.'-fatal:-Not-a-git-repository:-'.'-fatal:-Not-a-git-repository:-'.'-No-ruby-version-specified
 !     Valid versions: ruby-1.9.3-p0, ruby-1.9.3-p125, rbx-1.2.4, rbx-2.0.0dev-20120115-1.9, rbx-2.0.0dev-20120115-1.8, rbx-2.0.0dev-20120123-1.9, rbx-2.0.0dev-20120123-1.8, ruby-1.9.2-p290, jruby-1.6.5.1, jruby-1.6.7, ruby-1.9.3, ruby-1.9.2
 !
 !     Heroku push rejected, failed to compile Ruby/rails app

To git@heroku.com:myapp.git
 ! [remote rejected] tmp-heroku-deploy-gochez_heroku_test-2012-05-08-10-43-39 -> master (pre-receive hook declined)
error: failed to push some refs to 'git@heroku.com:myapp.git'

(Please note that I changed my real app name to myappfor privacy issues)

Any idea what could be causing this? Yesterday it worked perfectly. What debugging can I do to figure out what the problem is?