ASDM 6.1 contains this bug which sends an invalid configuration command to the PIX.
The solution is to enter the commands via the CLI interface which you can access via ASDM using the menu
Tools->Command Line Interface
Then enter the following commands to enable *all* threat detection statistics:
threat-detection statistics
For more information on securing your network with PIX firewall please see www.cisco.com/en/US/docs/security/asa/asa80/configuration/guide/protect.html