f5s flashing

hi guys after updating ajs list my f5s is now stuck on load, ive got a usb-rs232 tried lots of different f/w and erom updater checked all settings (ports etc) only goes as far as set stb memory error, borrowed a desktop uesd f-f rs232 serial null cable checked all settings and still end up at stb memory error, tried for about 6 hrs on both laptop (win8) and desktop(xp) with as many variations in timings as possible, even using a stopwatch to turn power on evry 1/4 of sec, AAAARRRRRGGGGHHHHHHHHHHHH!!!!!!!!!!!! :53_002:somebody HELP
thanks in advance, andy