Test Successful with 'Cannot start PhantomJS' Error

I'm get the strangest error with NodeJS v0.10.11 and karma tests via grunt.

Initially, the tests would not run as PhantomJS did not start. After updating NodeJS, I get this :

[2013-06-19 03:16:12.743] [DEBUG] config - autoWatch set to false, because of singleRun
INFO [karma]: Karma server started at http://localhost:8080/
INFO [launcher]: Starting browser PhantomJS
INFO [PhantomJS 1.9 (Linux)]: Connected on socket id KVDuQs5niBzzc8KQSnFm
PhantomJS 1.9 (Linux): Executed 1 of 1 SUCCESS (0.327 secs / 0.041 secs)
ERROR [launcher]: Cannot start PhantomJS

Why is there an error after the tests have run successfully ?

UPDATE: Adding code

Gruntfile karma task:

karma: {
      unit: {
        configFile: 'karma.conf.js',
        singleRun: true
      },
      e2e: {
        configFile: 'karma-e2e.conf.js',
        singleRun: true
      }
    }

karma.conf.js

// Karma configuration

// base path, that will be used to resolve files and exclude
basePath = '';

// list of files / patterns to load in the browser
// removed the following because of warning 'test/mock/**/*.js',
files = [
  JASMINE,
  JASMINE_ADAPTER,
  'app/components/angular/angular.js',
  'app/components/angular-mocks/angular-mocks.js',
  'app/scripts/*.js',
  'app/scripts/**/*.js',
  'test/spec/**/*.js'
];

// list of files to exclude
exclude = [];

// test results reporter to use
// possible values: dots || progress || growl
reporters = ['progress'];

// web server port
port = 8080;

// cli runner port
runnerPort = 9100;

// enable / disable colors in the output (reporters and logs)
colors = true;

// level of logging
// possible values: LOG_DISABLE || LOG_ERROR || LOG_WARN || LOG_INFO || LOG_DEBUG
logLevel = LOG_INFO;

// enable / disable watching file and executing tests whenever any file changes
autoWatch = false;

// Start these browsers, currently available:
// - Chrome
// - ChromeCanary
// - Firefox
// - Opera
// - Safari (only Mac)
// - PhantomJS
// - IE (only Windows)
browsers = ['PhantomJS'];

// If browser does not capture in given timeout [ms], kill it
captureTimeout = 5000;

// Continuous Integration mode
// if true, it capture browsers, run tests and exit
singleRun = false;