Most environments are setup so that when you log into unix you login through a profile that sets your default paths, etc for your session. cron does not get these unless you set them.
if your script is ksh you can put a statement in the script to set your environment... ie - if your default profile is the system profile in the /etc (maintained by the admin) you can put
. /etc/profile
in your script and it will set your environment for you. Note the space between the . and the /etc
If you then want to see your environment settings, you can use command set and put it out to a file.
example: set >/tmp/oc$$.set where oc$$ will be your proccess id.

Hope this helps