Github webhook delivery for github push event fails with 500 error

The circle build was starting correctly until I made some change to circle.yml file. It’s failing even after that code was reverted. The github webhook for push action returns 500 response with body “An internal server error occurred.”

Account settings
OS - Ubuntu 14.04 (Trusty)
2 containers (no parallelism)

Request URL:
Request method: POST
content-type: application/x-www-form-urlencoded
User-Agent: GitHub-Hookshot/886c556
X-GitHub-Event: push

Response Body
{“message”:“An internal server error occurred.”}

Response Headers
Connection: keep-alive
Content-Length: 48
Content-Type: application/json
Date: Thu, 16 Feb 2017 12:49:12 GMT
Server: nginx
X-Circleci-Request-Id: 1f532606-83da-4fde-926f-c68134a62dc0