PIX Device Manager (PDM) is supported only on PIX Software versions 6.0.1 and later.
To run PDM, you will need to upgrade your PIX software version to PIX 6.0 or later.
To read about system requirements needed to run PIX Software version 6.0.x and PDM, see Installing PDM on a PIX Firewall.
For more information please refer to the document Troubleshooting PIX Device Manager
PIX Device Manager Software Version