failing heroku buildpack

gistfile1.txt

> git push staging staging:master
Counting objects: 7, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (5/5), done.
Writing objects: 100% (5/5), 601 bytes, done.
Total 5 (delta 2), reused 0 (delta 0)

-----> Fetching custom git buildpack... done

 !     Heroku push rejected due to an unrecognized error.
 !     We've been notified, see http://support.heroku.com if the problem persists.


To git@heroku.com:balderton-staging.git
 ! [remote rejected] staging -> master (pre-receive hook declined)
error: failed to push some refs to 'git@heroku.com:balderton-staging.git'