acpi S3 not working

Me again,

I'd love to suspend my power hungry workstation but unfortunately 'acpiconf -s 
S3' doesn't work.
I only get: acpi0: device_suspend failed
If I don't load any kld (all my HW is kld) the system goes "black" and hangs.

Please find attached some additional info and this:

hw.acpi.supported_sleep_state: S3 S4 S5
hw.acpi.power_button_state: S5
hw.acpi.sleep_button_state: S3
hw.acpi.lid_switch_state: NONE
hw.acpi.standby_state: S1
hw.acpi.suspend_state: S3
hw.acpi.sleep_delay: 1
hw.acpi.s4bios: 0
hw.acpi.verbose: 0
hw.acpi.disable_on_reboot: 0
hw.acpi.handle_reboot: 0
hw.acpi.reset_video: 0
hw.acpi.cpu.cx_lowest: C1

Thanks,

-Harry