ERROR: dispatcher [dispatch.c:2635]: ds_options_callback() Setting the probing state failed (sip:10.0.9.133:5064, group 0)

I get this message periodically from 3 kamailio dispatchers simultaneously for the same destination host. Any idea what this error means? Dispatcher settings below:

modparam("dispatcher", "db_url", DBURL)
modparam("dispatcher", "table_name", "dispatcher")
modparam("dispatcher", "flags", 2)
modparam("dispatcher", "dst_avp", "$avp(dsdst)")
modparam("dispatcher", "grp_avp", "$avp(dsgrp)")
modparam("dispatcher", "cnt_avp", "$avp(dscnt)")
modparam("dispatcher", "dstid_avp", "$avp(dsdstid)")
modparam("dispatcher", "sock_avp", "$avp(dssocket)")
modparam("dispatcher", "attrs_avp", "$avp(dsattrs)")
modparam("dispatcher", "ds_hash_size", 3)
modparam("dispatcher", "force_dst", 1)
modparam("dispatcher", "ds_ping_interval", 20)
modparam("dispatcher", "ds_ping_from", "sip:pinger@MYPRIVATEIP:INTERNALPORT")
#modparam("dispatcher", "ds_ping_method", "INFO")
modparam("dispatcher", "ds_probing_mode", 1)
modparam("dispatcher", "ds_probing_threshold", 1)
modparam("dispatcher", "ds_ping_reply_codes", "class=2;code=480;code=404")