log4js Error: Cannot find module 'semver'

var log4js = require('node-log4js/log4js.js');
log4js.configure({
  appenders: [
    { type: 'console' },
    { type: 'file', filename: 'logs/cheese.log', category: 'cheese' }
  ]
});

log4js  Error: Cannot find module 'semver'

log4js 是正常加载了的，这个错误怎么回事啊！