The correct date and time must be set on the PIX for PIX Device Manager (PDM) to work. The date and time are used in the Secure Socket Layer (SSL) certificate for the PIX so that the browser can connect over SSL to the PIX for PDM. If the time is too far back or too far forward, then the certification will not be valid and the client's SSL session will not be allowed.
Use the PIX command line interface to correct the time with the setup command.
Delete the invalid certificate using the ca zeroize rsa command.