You're on server 2 (DirectAdmin), right? Change:
/home/polis/public_html/Sources/shop/dointerest.php
to:
/home/polis/domains/[yourdomain].frih.net/public_html/Sources/shop/dointerest.php
If this doesn't fix it, try /usr/local/bin/php, rather than /usr/bin/php.
I'm a moderator at FriHost, although I haven't been there for a while (and don't have much experience with Server 2 - I was hosted on Server 1)