As noted, (at least) Vixie's cron allows you to set environment variables. Some crons allow you to use the command field to set variables, thus:

ENV1=val ENV2=val command
[download]

Also, note that when you run from the command line your script has an open STDIN and an open STDOUT. In cron you do not have an open STDIN. STDOUT is generally a mail program. It is possible that cron errors are going to root. If you are not the admin, ask someone who is to see where cron errors go and if your script got any.

HTH, --traveler