New Roots user - running Grunt error

Hello all

Just starting out with Roots - looks good.

I have used Grunt on other projects and I have used Compass / SASS on other projects - but not LESS.

I thought I would just change the text colour variable in variables.less from @gray-dark to @gray-light;

I went to the root of my theme - called ‘gb_rrots’ and ran grunt.

Running “clean:dist” (clean) task
Cleaning assets/css/main.min.css…
Grunt aborted with the warning:
Warning - cannot delete files outside the current working directory

Any thoughts?

Thanks in advance