Core issue
This problem occurs when there is an incompatibility issue between the SNMP management station and the Pix software version.
Resolution
A Simple Network Management Protocol (SNMP) enhancement has been added to PIX Software release 6.0.1, allowing SNMP management stations to identify certain PIX models. For more information, refer to the CiscoView Support section of Release Notes for the Cisco Secure PIX Firewall Version 6.0(1).