can't import modules into a node script if it runs from cron

I have the module underscore installed globally with npm. if I run the script

/usr/local/bin/node /home/olmo/project/processDrivesMultiUser.js

it will run ok wherever I am on the path, but if I run a cronjob like this:

3,18,33,48, * * * * /usr/local/bin/node /home/olmo/project/processDrivesMultiUser.js

I get this error:

Date: Wed, 10 Sep 2014 16:26:01 -0600
From: Cron Daemon <root@db.local>
To: olmo@db.local
Subject: Cron <olmo@db> /usr/local/bin/node /home/olmo/project/processDrivesMultiUser.js


module.js:340
    throw err;
          ^
Error: Cannot find module 'underscore'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Module.require (module.js:364:17)
    at require (module.js:380:17)
    at Object.<anonymous> (/home/olmo/sandbox/api_ievwebapp/parseAdminScripts/processDrivesMultiUser.js:20:9)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)

somehow it can't find the module underscore if it runs via cron. I made the cron entry for the same username I'm using to run the script manually.

any ideas?