Index detected as System.register but didn't execute

StealJS
1

Why am I seeing this error:

TypeError: Error loading "testDist/bundles/test/index" at http://localhost:8080/testDist/bundles/test/index.js
testDist/bundles/test/index detected as System.register but didn't execute.
    at Loader.loader.instantiate (steal.js:3812)
    at Loader.loader.instantiate (steal.js:4153)
    at Loader.loader.instantiate (steal.js:4266)
    at Loader.loader.instantiate (steal.js:4590)
    at Loader.loader.instantiate (steal.js:4906)
    at Loader.loader.instantiate (steal.js:5743)
    at Loader.loader.instantiate (steal.js:5884)
    at Loader.loader.instantiate (steal.js:6000)
    at steal.js:1553
    at tryCatchReject (steal.js:1183)

when generating index.js using steal build using this config via grunt task:

{
        "options": {
          "steal": {
            "main": "test/index",
            "config": __dirname + "/package.json!npm"
          },
          "buildOptions": {
            "dest": "testDist",
            "minify": false,
            "bundleSteal": true
          }
        }
      }

and package.json as

"steal": {
    "plugins": [
      "steal-stache",
      "steal-less"
    ]
  }