I still get this error, because my project structure forces me to load the task from another location than the current one (via loadTasks("path/to/jsdoc-contrib")).
The task tries to resolve jsdoc based on the current path (cwd) and not from the script location (__dirname).
Changing the line
var base = 'node_modules/jsdoc/jsdoc',
var base = __dirname + '/../node_modules/jsdoc/jsdoc',
would fix this issue.
Humm, I'll think how to specify the jsdoc path as an option. I don't like the option relative to the task. I'll let you know.
Thanks for the report
You can set the jsdoc path as an option into your Gruntfile since 0.2.4