Script works when run from browser, but not in CronTab?

Question

i'm running ubuntu.

my cron job:

* * * * * cd /var/www/cron; php -f sendQueuedEmails.php

is set but is not running. when i run:

http://localhost/cron/sendQueuedEmails.php

inside firefox it works perfectly, but when i run:

php sendQueuedEmails.php

from the terminal, i get no errors and no output.

what could be the problem?