spawn: true = cannot find local grunt

[stevesweets]

Not entirely sure what caused this to be the case, but on osx, when using spawn: true, or omitting the setting entirely results in watch tasks that 'cannot find the local grunt'.

Grunt is installed globally, and if i run one of the watch tasks manually it does work.

Can repeat, in case you want me to try anything to give you further info.

Versions.

grunt-cli v0.1.13
grunt v0.4.5

And a dump of the thing in situ:

Running "copy:main" (copy) task
Copied 17 files

Running "watch" task
Waiting...
>> File "_build/less/_main.less" changed.
grunt-cli: The grunt command line interface. (v0.1.13)

Fatal error: Unable to find local grunt.

If you're seeing this message, either a Gruntfile wasn't found or grunt
hasn't been installed locally to your project. For more information about
installing and configuring grunt, please see the Getting Started guide:

http://gruntjs.com/getting-started
Completed in 0.203s at Mon Apr 20 2015 15:19:00 GMT+0100 (BST) - Waiting...