Freeradius3 error: "Failed to find pap as a module or policy"


When I try to run freeradius3 server, LD_LIBRARY_PATH=/usr/lib/freeradius3 radiusd -X
I got the following error:

# Loading authenticate {...}
/etc/freeradius3/sites-enabled/default[489]: Failed to find "pap" as a module or policy.
/etc/freeradius3/sites-enabled/default[489]: Please verify that the configuration exists in /etc/freeradius3/mods-enabled/pap.
/etc/freeradius3/sites-enabled/default[489]: Failed to parse "pap" entry.

Anyone has any idea of how to resolve the issue.