problem with bash script

[Paolo De Michele]

hi everybody,

I have a problem with my bash script.
this script will do a backup in a particular directory - look below:

#

BCK_FILE=/backup/www/test
destinatario=alert at piludu.it

sites=("client1/web1" "client1/web2")
sito=("1" "2")

tLen=${#sites[@]}

for (( i=0; i<${tLen}; i++ ));
do

cd /var/www/clients/
cp -R ${sites[$i]} /backup/temp/www/
cd /backup/temp/www/

tar cfz `date +%F`_web${sito[$i]}.tar.gz web${sito[$i]}/

mv *.tar.gz /backup/www/test/

rm -rf /backup/temp/www/*

done


if I start this script.sh in my console 
# ./script.sh it works 
but if I schedule it in my crontab doesn't work 

what is the problem?
can I fix it?

thanks in advance
regards