Fisrt try it by repairing the eximstat DB, then restart the tailwatchd service, if no go follow the steps,
mv /var/cpanel/sql/eximstats.sql /var/cpanel/sql/eximstats.sql.tmp_working_copy
/usr/local/cpanel/libexec/tailwatch/tailwatchd --restart
mysql eximstats < /var/cpanel/sql/eximstats.sql.tmp_working_copy
Ref: http://forums.hostgator.com/whm-emails-view-relayers-t118597.html?s=5cc2dfb6f6b7f8fb2b7a503067c827f7&