Check for incoming icmp log from hosts configured on the pix. Could be
- a misconfigured server the pix cannot reach
- a patch not well applied on syslog-server or snmp-server.
- misconfgured pix eg wrong ip server-address,
- port udp/514 not opened on server, etc...
Check either the syslog-server and snmp-server.
As a permanent workaround, enable icmp echo and icmp echo reply for the faulty host.