Hi,
Does this scenario / solution apply to your circumstance:
The %PIX-4-402101: decaps: recd IPSEC packet has invalid spi for destaddr=dest_address, prot=protocol, spi=number error message is received on the PIX Firewall
VERSION 2
Core issue
The received IPsec packet specifies a security parameters index (SPI) that does not exist in the security association database (SADB). This can be a temporary condition due to slight differences in the aging of security associations (SAs) between the IPsec peers or it can be due to the clearing of the local SAs. This condition can also be caused by incorrect packets sent by the IPsec peer.
Note: This can also be an attack.
Resolution
The peer may not acknowledge that the local SAs have been cleared. If a new connection is established from the local router, the two peers can then reestablish successfully. Otherwise, if the problem occurs for more than a brief period, either attempt to establish a new connection or contact the peer's administrator.
For more information about PIX Firewall syslog messages, refer to Cisco PIX Firewall System Log Messages, Version 6.3 and Cisco Security Appliance System Log Messages, Version 7.0.
