You are using the SST 27SF512. To erase that part you need to pull the CE# pin low then apply a voltage of 11.4 to 12 V to the OE#/Vpp and A9 pins.
If you are having trouble getting the verification values of FFH afterward make sure you are getting the voltage you need to the OE#/Vpp and A9 pins. Without that voltage the device wont erase.
Look at this to make sure you have followed the programmers instructions for switch settings and jumper placements. http://forum.pgmfi.org/viewtopic.php...b609385bb1cd2d