The PIX Firewall may randomly reload when processing Internet Control Message Protocol (ICMP) error packets.
This issue occurs in Cisco PIX/ASA running release 7.0.4. This could happen with or without the inspect icmp error in the configuration.
This issue is documented in Cisco bug ID CSCsc81236.
To resolve this issue, downgrade the IOS version to 7.0.2.
The issue has been fixed in PIX IOS version 7.1(0.182).