the provided default file has an incorrect path (and seems to be duplicated) to the python script:
# The check_my_reputation.py script can be run on any host, but requires you to
# enable stuff in reputation.conf
#
[script://$SPLUNK_HOME\etc\apps\fwd_reputation\bin\check_my_reputation.py]
source=Senderbase
sourcetype=MSExchange:Reputation
interval=14400
index=msexchange
disabled=true
[script://$SPLUNK_HOME/etc/apps/fwd_reputation/bin/check_my_reputation.py]
source=Senderbase
sourcetype=MSExchange:Reputation
interval=14400
index=msexchange
disabled=false
Looks like this file needs to be updated from the beta to:
[script://$SPLUNK_HOME/etc/apps/TA-SMTP-Reputation/bin/check_my_reputation.py
Thanks for the bug report. I've filed a bug against this one and it will be incorporated in the next release of the app.