Why does my S700 not work with the POS I/O expansion card? When the card is plugged in, the servo amplifier doesn't boot.

The card exists with different versions, visible on a label on the card's PCB.

With the current version (Nov. 08) "ROD in/out; SSI in/out" is marked on the label and the S700 needs at least Firmware 3.50. 

If "ROD out" is marked or no label exists, you have an older version, which can only be operated with an older firmware (3.06). Updating the card to the current version is possible at the manufacturer site.