General "Script error" in console. (Karma version: 0.13.21)

### Expected behavior

Tests should run and either pass or fail.
### Actual behavior

Randomly, when running our tests via Grunt, we sometimes get a Script error in the console. But, then if we try running again, the script error does NOT occur and tests will run and fail / pass properly. This is an important issue because while we can run tests locally as many times as we want in development, the CI server runs the tests once and then the builds fail as a result. We then have to manually try to rerun the CI server to make a build pass.
### Enviroment Details

Karma version: 0.13.21
karma-phantomjs-launcher 0.2.1
PhantomJS 1.9.18
grunt-cli v0.1.13
grunt v0.4.5
Mac OS X 10.10.5
### Steps to reproduce the behavior
1. It seems like when we make changes to our tests, or add new tests, the first time we run the tests we get the Script error. But, then if we try running again, the script error does NOT occur and tests will run and fail or pass properly. This is an important issue because while we can run tests locally as many times as we want in development, the CI server runs the tests and builds fail as a result. We then will have to manually try to rerun the CI server to make a build pass.


Start by running the tests through Grunt with Karma 0.13.21, karma-phantomjs-launcher 0.2.1, and PhantomJS 1.9.18, comparing the first run after test changes with subsequent runs. Investigate the intermittent console "Script error" and confirm that the test command completes reliably on the first CI run.

Written by the indexing model from the issue text.