Grunt Concat cannot write to file

view story

http://stackoverflow.com – Just installed latest Grunt on Ubuntu 12.04. Here is my gruntfile: module.exports = function(grunt){ //project configuration grunt.initConfig({ pkg: grunt.file.readJSON('package.json'), concat: { slides : { src : ['src/top.html', 'src/bottom.html'], dest : ['build/index.html'] } } }); //enable plugins grunt.loadNpmTasks('grunt-contrib'); grunt.registerTask('default', ['concat:slides']); } This creates the build/ directory fine, but gives me the output of: Running "concat:slides" (concat) task Warning: Unable to write "build/index. (HowTos)